U.S. patent number 9,971,266 [Application Number 15/440,573] was granted by the patent office on 2018-05-15 for method of producing toner for developing electrostatic images.
This patent grant is currently assigned to KONICA MINOLTA, INC.. The grantee listed for this patent is Konica Minolta, Inc.. Invention is credited to Atsushi Iioka, Takanari Kayamori, Masaharu Matsubara, Kouji Sekiguchi, Naoya Tonegawa.
United States Patent |
9,971,266 |
Tonegawa , et al. |
May 15, 2018 |
Method of producing toner for developing electrostatic images
Abstract
A method of producing a toner for developing electrostatic
images includes Steps I to III is provided. The toner includes a
toner matrix particle having a core-shell structure. The toner
matrix particle includes a core particle including an amorphous
resin A and a crystalline material, and a shell including an
amorphous resin B. The shell includes a phase of the amorphous
resin B that is not fused with the core particle at the interface.
The amorphous resin A differs from the amorphous resin B.
Inventors: |
Tonegawa; Naoya (Sagamihara,
JP), Kayamori; Takanari (Kawasaki, JP),
Matsubara; Masaharu (Hachioji, JP), Sekiguchi;
Kouji (Tokyo, JP), Iioka; Atsushi (Hachioji,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Konica Minolta, Inc. |
Tokyo |
N/A |
JP |
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Assignee: |
KONICA MINOLTA, INC. (Tokyo,
JP)
|
Family
ID: |
59722193 |
Appl.
No.: |
15/440,573 |
Filed: |
February 23, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170255115 A1 |
Sep 7, 2017 |
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Foreign Application Priority Data
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Mar 2, 2016 [JP] |
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2016-039577 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03G
9/09328 (20130101); G03G 9/09321 (20130101); G03G
9/09364 (20130101); G03G 9/09371 (20130101); G03G
9/09392 (20130101) |
Current International
Class: |
G03G
9/093 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2011257526 |
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Dec 2011 |
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JP |
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2012194314 |
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Oct 2012 |
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JP |
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2014102446 |
|
Jun 2014 |
|
JP |
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WO-2011021675 |
|
Feb 2011 |
|
WO |
|
Primary Examiner: Rodee; Christopher D
Attorney, Agent or Firm: Lucas & Mercanti, LLP
Claims
What is claimed is:
1. A method of producing a toner for developing electrostatic
images, the toner comprising a toner matrix particle having a
core-shell structure, wherein the toner matrix particle comprising
a core particle comprising an amorphous resin A and a crystalline
material, and a shell comprising an amorphous resin B, the shell
comprising a phase of the amorphous resin B that is not fused with
the core particle at the interface, and the amorphous resin A
differing from the amorphous resin B, the method comprising the
steps of: Step I) dispersing at least the amorphous resin A and the
crystalline material in an aqueous medium to prepare a dispersion,
and adjusting a temperature of the dispersion to be equal to or
higher than (a glass transition temperature (T.sub.g-a) of the
amorphous resin A+10).degree. C. and equal to or lower than (a
melting point (T.sub.m-c) of the crystalline material+10).degree.
C., to prepare a core particle dispersion through coagulation and
coalescence of at least the amorphous resin A and the crystalline
material; Step II) cooling the core particle dispersion prepared in
Step I to a temperature equal to or lower than the glass transition
temperature (T.sub.g-a) of the amorphous resin A; and Step III)
adjusting a temperature of the core particle dispersion to be equal
to or higher than (the glass transition temperature (T.sub.g-a) of
the amorphous resin A+5).degree. C. and equal to or lower than (a
glass transition temperature (T.sub.g-b) of the amorphous resin
B+3).degree. C. after Step II, and then adding a dispersion of the
amorphous resin B to the core particle dispersion, wherein
Expressions 1 and 2 are satisfied in Step III:
pH.sub.b.ltoreq.pH.sub.a, and Expression 1:
2.ltoreq.pH.sub.b.ltoreq.5 Expression 2: where pH.sub.a represents
the pH of the core particle dispersion at 25.degree. C., and
pH.sub.b represents the pH of the dispersion of the amorphous resin
B at 25.degree. C.
2. The method according to claim 1, wherein the core particle
dispersion cooled in Step II contains a core particle having a
shape factor SF-2 of 105 to 140.
3. The method according to claim 1, wherein the amorphous resin B
added in Step III is a particle having a volume median particle
size of 30 to 300 rm.
4. The method according to claim 1, wherein the amorphous resin A
is a styrene-acrylic resin, and the amorphous resin B is a
polyester resin.
5. The method according to claim 1, wherein the amorphous resin A
is a polyester resin, and the amorphous resin B is a
styrene-acrylic resin.
6. The method according to claim 4, wherein the polyester resin is
an amorphous polyester resin chemically bonded to a styrene-acrylic
resin.
7. The method according to claim 5, wherein the polyester resin is
an amorphous polyester resin chemically bonded to a styrene-acrylic
resin.
8. The method according to claim 6, wherein the amorphous polyester
resin chemically bonded to the styrene-acrylic resin has a
styrene-acrylic content of 5 to 30 mass %.
9. The method according to claim 7, wherein the amorphous polyester
resin chemically bonded to the styrene-acrylic resin has a
styrene-acrylic content of 5 to 30 mass %.
10. The method according to claim 1, wherein the amorphous resin A
has a glass transition temperature T.sub.g-a of 35 to 50.degree.
C.
11. The method according to claim 1, wherein the amorphous resin B
has a glass transition temperature T.sub.g-b of 53 to 63.degree.
C.
12. The method according to claim 1, wherein the crystalline
material comprises a crystalline resin or a release agent, if the
crystalline material is the releasing agent then the releasing
agent is one selected from the group consisting of a hydrocarbon
wax and an ester wax, and the crystalline material has a melting
point (T.sub.m-c) equal to or higher than (a glass transition
temperature (T.sub.g-b) of the amorphous resin B+3).degree. C.
13. The method according to claim 1, wherein the ratio of the mass
of the amorphous resin B added in Step III to the total mass of a
binder resin is 5 to 35, and the binder resin comprises amorphous
resin A and amorphous resin B.
Description
This application is based on Japanese Patent Application No.
2016-039577 filed on Mar. 2, 2016 with Japan Patent Office, the
entire content of which is hereby incorporated by reference.
1. FIELD OF THE INVENTION
The present invention relates to a method of producing a toner for
developing electrostatic images. In particular, the present
invention relates to a method of producing a toner for developing
electrostatic images, the toner having high compatibility between
thermal resistance during storage and low-temperature fixing
properties, exhibiting improved charging properties, and providing
high-quality images.
2. DESCRIPTION OF RELATED ART
A toner matrix particle has been proposed which exhibits
compatibility between low-temperature fixing properties and thermal
resistance during storage and has a structure including a core
particle coated with a shell (hereinafter the structure may be
referred to as "core-shell structure"). In the matrix particle
having a core-shell structure, the core particle generally melts at
low temperatures and the shell generally exhibits thermal
resistance during storage.
The toner matrix particle contains an amorphous resin, such as a
polyester resin exhibiting high compatibility between thermal
resistance and fixing properties, or a styrene-acrylic resin having
superior anti-charging properties and prepared from a
general-purpose monomer at low cost.
Another toner matrix particle has been proposed which includes a
core particle and a shell composed of different amorphous resins;
for example, a core particle composed of an amorphous vinyl resin
(or polyester resin) and a shell composed of an amorphous polyester
resin (or vinyl resin), such that the core particle and the shell
exhibits different characteristics.
For example, Japanese Unexamined Patent Application Publication No.
2012-194314 discloses a toner matrix particle including a core
particle containing a polyester resin and a shell containing a
vinyl copolymer (styrene-acrylic) resin. Unfortunately, in the
toner matrix particle including the core particle and shell
composed of different resins, the compatibility between the core
particle and the shell is lower than that in the case where the
core particle and the shell are composed of the same resin, and
small discrete segments of the shell lie on the surface of the core
particle and form convex portions. Thus, the core particle has many
exposed portions, resulting in insufficient thermal resistance
during storage. In addition, the core particle cannot be evenly
coated with an external additive because of the rough surface of
the toner matrix particle. Thus, the toner including the core
particle may fail to exhibit satisfactory charging properties.
Japanese Unexamined Patent Application Publication No. 2014-102446
discloses a toner including a core particle and a shell composed of
an inner layer and an outer layer, wherein the inner layer contains
a resin having a solubility parameter (SP) falling within a range
between the SP of a resin contained in the core particle and the SP
of a resin contained in the outer layer.
Although the resins contained in the inner and outer layers and the
core particle have similar SP values, the structure of the resin
contained in the core particle still differs from that of the resin
contained in the shell, and satisfactory effects was not able to be
achieved.
Japanese Unexamined Patent Application Publication No. 2011-257526
discloses a toner including a modified polyester resin containing a
styrene-acrylic resin chemically bonded to a polyester resin.
Although the technique disclosed in Japanese Unexamined Patent
Application Publication No. 2011-257526 achieves high compatibility
between a core particle and a shell, the shell may be composed of
non-coated rough domains, resulting in unsatisfactory thermal
resistance during storage. Alternatively, a release agent or a
colorant may be insufficiently dispersed in the toner, resulting in
unsatisfactory charging properties or image quality (e.g., low
transfer efficiency at high temperature and high humidity and low
GI level).
Thus, a further improvement is required for forming a shell coat or
a coat domain on the surface of a core particle such that the shell
and the core particle exhibit different functions to enhance the
quality of the resultant toner.
SUMMARY OF THE INVENTION
An object of the present invention, which has been conceived in
light of the problems and circumstances described above, is to
provide a method of producing a toner for developing electrostatic
images, the toner having high compatibility between thermal
resistance during storage and low-temperature fixing properties,
exhibiting improved charging properties, and providing high-quality
images.
The present inventors have conducted studies for solving the
aforementioned problems and have developed a method of producing a
toner for developing electrostatic images, the method involving
synthesis of toner matrix particles under specific conditions
(e.g., temperature ranges) described below in Steps I to III. The
inventors have found that the toner produced by the method has high
compatibility between thermal resistance during storage and
low-temperature fixing properties, exhibits improved charging
properties, and provides high-quality images. The present invention
has been accomplished on the basis of this finding.
The present invention to solve the problems described above is
characterized by the following aspects.
1. A method of producing a toner for developing electrostatic
images, the toner including a toner matrix particle having a
core-shell structure, wherein
the toner matrix particle including a core particle including an
amorphous resin A and a crystalline material, and a shell including
an amorphous resin B,
the shell including a phase of the amorphous resin B that is not
fused with the core particle at the interface, and
the amorphous resin A differing from the amorphous resin B, the
method including the steps of:
Step I) dispersing at least the amorphous resin A and the
crystalline material in an aqueous medium to prepare a dispersion,
and adjusting a temperature of the dispersion to be equal to or
higher than (a glass transition temperature (T.sub.g-a) of the
amorphous resin A+10).degree. C. and equal to or lower than (a
melting point (T.sub.m-c) of the crystalline material+10).degree.
C., to prepare a core particle dispersion through coagulation and
coalescence of at least the amorphous resin A and the crystalline
material;
Step II) cooling the core particle dispersion prepared in Step I to
a temperature equal to or lower than the glass transition
temperature (T.sub.g-a) of the amorphous resin A; and
Step III) adjusting a temperature of the core particle dispersion
to be equal to or higher than (the glass transition temperature
(T.sub.g-a) of the amorphous resin A+5).degree. C. and equal to or
lower than (a glass transition temperature (T.sub.g-b) of the
amorphous resin B+3).degree. C. after Step II, and then adding a
dispersion of the amorphous resin B to the core particle
dispersion.
2. The method according to item 1, wherein Expressions 1 and 2 are
satisfied in Step III: pH.sub.b.ltoreq.pH.sub.a, and Expression 1:
2.ltoreq.pH.sub.b.ltoreq.5 Expression 2: where pH.sub.a represents
the pH of the core particle dispersion at 25.degree. C., and
pH.sub.b represents the pH of the dispersion of the amorphous resin
B at 25.degree. C. 3. The method according to item 1, wherein the
core particle dispersion cooled in Step II contains a core particle
having a shape factor SF-2 of 105 to 140. 4. The method according
to item 1, wherein the amorphous resin B added in Step III is a
particle having a volume median particle size of 30 to 300 nm. 5.
The method according to item 1, wherein the amorphous resin A is a
styrene-acrylic resin, and the amorphous resin B is a polyester
resin. 6. The method according to item 1, wherein the amorphous
resin A is a polyester resin, and the amorphous resin B is a
styrene-acrylic resin. 7. The method according to item 5, wherein
the polyester resin is an amorphous polyester resin chemically
bonded to a styrene-acrylic resin. 8. The method according to item
6, wherein the polyester resin is an amorphous polyester resin
chemically bonded to a styrene-acrylic resin. 9. The method
according to item 7, wherein the amorphous polyester resin
chemically bonded to the styrene-acrylic resin has a
styrene-acrylic content of 5 to 30 mass %. 10. The method according
to item 8, wherein the amorphous polyester resin chemically bonded
to the styrene-acrylic resin has a styrene-acrylic content of 5 to
30 mass %. 11. The method according to item 1, wherein the
amorphous resin A has a glass transition temperature T.sub.g-a of
35 to 50.degree. C. 12. The method according to item 1, wherein the
amorphous resin B has a glass transition temperature T.sub.g-b of
53 to 63.degree. C. 13. The method according to item 1, wherein the
crystalline material includes a crystalline resin or a release
agent selected from a hydrocarbon wax and an ester wax, and the
crystallin e material has a melting point (T.sub.m-c) equal to or
higher than (a glass transition temperature (T.sub.g-b) of the
amorphous resin B+3).degree. C. 14. The method according to item 1,
wherein the ratio of the mass of the amorphous resin B added in
Step III to the total mass of a binder resin is 5 to 35.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a toner matrix
particle according to the present invention.
FIG. 2 is an electron microscopic cross-sectional view of a toner
matrix particle according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method of producing a toner for
developing electrostatic images, the toner including a toner matrix
particle having a core-shell structure. The toner matrix particle
includes a core particle including an amorphous resin A and a
crystalline material, and a shell including an amorphous resin B.
The shell includes a phase of the amorphous resin B that is not
fused with the core particle at the interface. The amorphous resin
A differs from the amorphous resin B. The method includes Steps I
to III described above. These technical characteristics are common
in aspects of the present invention.
The mechanisms and operations that establish the advantageous
effects of the present invention are inferred as described
below.
Since the surface irregularities of the core particles can be
reduced through coagulation and coalescence of the amorphous resin
A and the crystalline material at a temperature described in Step I
according to the present invention, matrix particles having a
core-shell structure can be prepared from a minimal amount of the
resin for shells. Thus, the toner for developing electrostatic
images (hereinafter may be referred to simply as "toner") of the
present invention exhibits compatibility between thermal resistance
during storage and low-temperature fixing properties. The core
particles can be prepared such that a release agent or a colorant
is dispersed in the amorphous resin matrix. Accordingly, the
resultant toner exhibits superior charging properties and provides
high-quality images.
Since the core particles prepared through Step I can be coagulated
with and deposited to particles of the amorphous resin B in Steps
II and III according to the present invention, the resultant toner
exhibits superior charging properties and provides high-quality
images. The shell particles composed of the amorphous resin B are
deposited onto the surfaces of the core particles while the
particle size of the shell particles is maintained. Thus, during
coagulation between the core particles and the shell particles, the
shell particles form coat domains (rather than non-coated rough
domains) to cover the surfaces of the core particles. The resultant
toner exhibits superior thermal resistance during storage and
charging properties.
As described above, Steps I to III of the method of the present
invention involve coagulation and coalescence of different
amorphous resins (i.e., a vinyl resin, such as a styrene-acrylic
resin, and an amorphous polyester resin) in an aqueous medium to
prepare toner matrix particles having a core-shell structure. In
these steps, the shell particles composed of the amorphous resin B
maintain their form and appropriately coagulate and coat the
surfaces of the core particles, resulting in prevention of
formation of large particles (domain formation) due to fusion of
the shell particles, or intrusion of the shell particles into cores
during formation of core-shell composite particles. Thus, the
shells form coating layers or coat domains on the surfaces of the
toner matrix particles, and the resultant toner for developing
electrostatic images exhibits superior thermal resistance during
storage and improved charging properties, and provides high-quality
images.
In the present invention, Expressions 1 and 2 are preferably
satisfied in Step III: pH.sub.b.ltoreq.pH.sub.a, and Expression 1:
2.ltoreq.pH.sub.b.ltoreq.5 Expression 2: where pH.sub.a represents
the pH of the core particle dispersion at 25.degree. C., and
pH.sub.b represents the pH of the dispersion of the amorphous resin
B at 25.degree. C. This leads to formation of a homogeneous shell
deposition layer, resulting in enhanced thermal resistance to a
maximal degree during storage.
In the present invention, the dispersion cooled in Step II
preferably contains a core particle having a shape factor SF-2 of
105 to 140. This leads to high compatibility between thermal
resistance during storage and low-temperature fixing
properties.
In the present invention, the amorphous resin B added in Step III
is preferably in the form of particles having a volume median
particle size of 30 to 300 nm in view of even deposition of the
shell and preparation of the shell from a small amount of
resin.
In the present invention, preferably, the amorphous resin A is a
styrene-acrylic resin and the amorphous resin B is a polyester
resin, or the amorphous resin A is a polyester resin and the
amorphous resin B is a styrene-acrylic resin. Such a combination of
the amorphous resin A and the amorphous resin B is more suitable
for formation of domains of the amorphous resin contained in the
shell on the surface layer of the toner particle or in the interior
of the particle. Thus, the toner for developing electrostatic
images produced by the method exhibits superior thermal resistance
during storage and improved charging properties and provides
high-quality images.
In the present invention, the polyester resin is preferably an
amorphous polyester resin chemically bonded to a styrene-acrylic
resin in view of an improvement in toner retention after fixation
of toner particles.
In the present invention, the amorphous polyester resin chemically
bonded to the styrene-acrylic resin preferably has a
styrene-acrylic content of 5 to 30 mass % in view of an improvement
in releasability of the toner during fixation, and high toner
retention after fixation.
In the present invention, the amorphous resin A preferably has a
glass transition temperature T.sub.g-a of 35 to 50.degree. C. in
view of achievement of low-temperature fixing properties.
In the present invention, the amorphous resin B preferably has a
glass transition temperature T.sub.g-b of 53 to 63.degree. C. in
view of achievement of thermal resistance during storage.
In the present invention, the crystalline material preferably
includes a crystalline resin or a release agent selected from a
hydrocarbon wax and an ester wax, and the crystalline material
preferably has a melting point (T.sub.m-c) equal to or higher than
(the glass transition temperature (T.sub.g-b) of the amorphous
resin B+3).degree. C., in view of a further improvement in thermal
resistance during storage and transfer efficiency.
In the present invention, the ratio of the mass of the amorphous
resin B added in Step III to the total mass of the binder resin is
preferably 5 to 35 in view of improvements in thermal resistance
during storage and releasability during fixation of the toner.
The present invention, its components, and embodiments and aspects
for implementing the present invention will now be described in
detail. As used herein, the term "to" between two numerical values
indicates that the numeric values before and after the term are
inclusive as the lower limit value and the upper limit value,
respectively.
<<Method of Producing Toner for Developing Electrostatic
Images>>
The present invention provides a method of producing a toner for
developing electrostatic images, the toner including toner matrix
particles each having a core-shell structure. The toner matrix
particles each include a core particle including an amorphous resin
A and a crystalline material, and a shell including an amorphous
resin B. The shell includes a phase of the amorphous resin B that
is not fused with the core particle at the interface. The amorphous
resin A differs from the amorphous resin B. The method includes
Steps I to III described below.
Step I involves dispersing at least the amorphous resin A and the
crystalline material in an aqueous medium to prepare a dispersion,
and adjusting the temperature of the dispersion to be equal to or
higher than (the glass transition temperature (T.sub.g-a) of the
amorphous resin A+10).degree. C. and equal to or lower than (the
melting point (T.sub.m-c) of the crystalline material+10).degree.
C., to prepare a core particle dispersion through coagulation and
coalescence of at least the amorphous resin A and the crystalline
material.
Step II involves cooling the core particle dispersion prepared in
Step I to a temperature equal to or lower than the glass transition
temperature (T.sub.g-a) of the amorphous resin A.
Step III involves adjusting the temperature of the core particle
dispersion to be equal to or higher than (the glass transition
temperature (T.sub.g-a) of the amorphous resin A+5).degree. C. and
equal to or lower than (the glass transition temperature
(T.sub.g-b) of the amorphous resin B+3).degree. C. after Step II,
and then adding a dispersion of the amorphous resin B to the core
particle dispersion.
In the method of the present invention, the glass transition
temperature (T.sub.g-a) of the amorphous resin A, the melting point
(T.sub.m-c) of the crystalline material, and the glass transition
temperature (T.sub.g-b) of the amorphous resin B are determined as
described below. The glass transition temperature (T.sub.g-a) of
the amorphous resin A, the melting point (T.sub.m-c) of the
crystalline material, or the glass transition temperature
(T.sub.g-b) of the amorphous resin B can be controlled by
adjustment of the composition (proportions) of monomers for the
resin or the molecular weight of the resin.
(Measurement of Melting Point (T.sub.m-c) of Crystalline
Material)
The melting point of the crystalline material in the toner can be
measured with a differential scanning calorimeter "Diamond DSC"
(manufactured by PerkinElmer, Inc.). In detail, a sample of the
toner (3.0 mg) was sealed in an aluminum pan and placed on a sample
holder of the calorimeter. The calorimetry was performed by the
following temperature program: a first heating process involving
heating from room temperature (25.degree. C.) to 150.degree. C. at
a rate of 10.degree. C./min and maintaining at 150.degree. C. for
five minutes; a cooling process involving cooling from 150.degree.
C. to 0.degree. C. at a rate of 10.degree. C./min and maintaining
at 0.degree. C. for five minutes; and a second heating process
involving heating from 0.degree. C. to 150.degree. C. at a rate of
10.degree. C./min. An empty aluminum pan was used as a
reference.
An endothermic curve prepared through the first heating process was
analyzed, and the maximum temperature of the endothermic peak of
the crystalline material was defined as the melting point T.sub.m-c
(.degree. C.) of the crystalline material. An exothermic curve
prepared through the cooling process was analyzed, and the maximum
temperature of the exothermic peak of the crystalline material was
defined as T.sub.q-c (.degree. C.).
(Measurement of Glass Transition Temperature T.sub.g of Amorphous
Resin)
The glass transition temperature (T.sub.g-a) of the amorphous resin
A and the glass transition temperature (T.sub.g-b) of the amorphous
resin B can be determined with a differential scanning calorimeter
"Diamond DSC" (manufactured by PerkinElmer, Inc.). The temperature
of a sample is controlled through sequential processes of heating,
cooling, and heating (temperature range: 0 to 150.degree. C.,
heating rate: 10.degree. C./minute, cooling rate: 10.degree.
C./minute). The glass transition temperature can be determined on
the basis of the data obtained through the second heating process.
In detail, the glass transition temperature corresponds to the
intersection of a line extending from the base line of the first
endothermic peak and a tangent corresponding to the maximum slope
between the rising point and maximum point of the first endothermic
peak.
Now will be described components of toner matrix particles and an
external additive, the toner matrix particles having a core-shell
structure and contained in the toner for developing electrostatic
images produced by the method of the present invention and then
detailed description of Steps I to III.
[Toner Matrix Particle Having Core-Shell Structure]
The toner matrix particles according to the present invention each
have a core-shell structure (hereinafter the particles may be
referred to as "core-shell toner matrix particles"). The core-shell
structure is composed of a core particle and a shell covering the
core particle. The shell may be composed of a large-area coat
(hereinafter may be referred to as "shell coat") or several domains
of a coat (hereinafter may be referred to as "coat domains").
Unless otherwise specified, the shell coat and the coat domains
will be collectively referred to as "shell."
An external additive is optionally applied to the toner matrix
particles. The toner matrix particles having the external additive
may be used as toner particles. Alternatively, the toner matrix
particles having no external additive may be used as toner
particles. The toner is composed of such toner particles.
The core particle contains the amorphous resin A and the
crystalline material.
The shell contains the amorphous resin B. The shell is composed of
a phase of the amorphous resin B that is not fused with the core
particle at the interface. The shell and the core particle may be
partially fused with each other at the interface therebetween so
long as the advantageous effects of the present invention are not
inhibited. The presence of such a fused portion probably
contributes to further improvements in fracture resistance and
toughness of the toner matrix particles.
The amorphous resin A contained in the core particle differs from
the amorphous resin B contained in the shell.
FIG. 1 is a schematic cross-sectional view of a toner matrix
particle according to an embodiment of the present invention
captured with an electron microscope by the method described below.
FIG. 2 is a cross-sectional image of a toner matrix particle.
As illustrated in FIG. 1, a toner matrix particle 1 includes a core
particle 2 and a shell 3 covering the surface of the core particle
2. The shell 3 is composed of one or more coat domains 31.
The thick solid line represents the interface I.sub.se between the
shell and an embedding resin described below. The thin solid line
represents the interface I.sub.ce between the core particle and the
embedding resin. The dotted line represents the interface I.sub.cs
between the core particle and the shell.
In the toner matrix particle 1 according to the present invention,
the shell preferably has a continuous phase; i.e., no cracks in
each of the coat domains 31 (like the case shown in FIG. 1), in
view of preventing excess elution of the components contained in
the core particle 2 through such cracks.
[Amorphous Resin]
The amorphous resin has a glass transition point (T.sub.g) but no
melting point (i.e., no clear endothermic peak during temperature
elevation) in an endothermic curve prepared by differential
scanning calorimetry (DSC).
The amorphous resins A and B usable in the present invention are
described below. In the toner matrix particles according to the
present invention, the amorphous resin A contained in the core
particle differs from the amorphous resin B contained in the shell
as described above.
As used herein, the amorphous resin A, the amorphous resin B, and
the crystalline resin described below may be collectively referred
to as "binder resin." Thus, the total mass of the binder resin
corresponds to the total mass of the amorphous resin A, the
amorphous resin B, and the crystalline resin.
As used herein, the term "different amorphous resins" refers to
amorphous resins composed of different types of monomers, and does
not refer to amorphous resins having different monomer proportions
or amorphous resins having different degrees of modification (e.g.,
styrene-acrylic modified polyester resins described below). In the
core-shell toner containing different amorphous resins (i.e., the
amorphous resin A and the amorphous resin B), the core particle or
the shell layer contains different amorphous resin components in an
amount of 50% or more.
Different types of resins may be detected by any known technique;
for example, staining described in Examples, or atomic force
microscopy (AFM) for determining the hardness or infrared
wavelength of a resin present in a cross section.
The amorphous resin may be of any type, such as a styrene-acrylic
resin or an amorphous polyester resin.
Preferably, the amorphous resin A is a styrene-acrylic resin and
the amorphous resin B is a polyester resin, or the amorphous resin
A is a polyester resin and the amorphous resin B is a
styrene-acrylic resin. Such a combination of the amorphous resin A
and the amorphous resin B is more suitable for formation of domains
of the amorphous resin contained in the shell on the surface layer
of the toner particle or in the interior of the particle. Thus, the
method of the present invention can produce a toner for developing
electrostatic images exhibiting superior thermal resistance during
storage and improved charging properties and providing high-quality
images.
Particularly preferably, the amorphous resin A is a styrene-acrylic
resin and the amorphous resin B is a polyester resin, in view of
production of a toner exhibiting charging properties stable against
environmental variations (e.g., variations in humidity and
temperature) and having superior low-temperature fixing
properties.
In view of low-temperature fixing properties, the amorphous resin A
has a glass transition temperature T.sub.g-a of preferably 35 to
50.degree. C., more preferably 38 to 48.degree. C.
In view of thermal resistance during storage, the amorphous resin B
has a glass transition temperature T.sub.g-b of preferably 53 to
63.degree. C., more preferably 56 to 62.degree. C.
<Styrene-Acrylic Resin>
The styrene-acrylic resin is prepared through polymerization of a
styrene monomer and an acrylic monomer.
The styrene-acrylic resin preferably has a weight average molecular
weight (Mw) of 25,000 to 60,000 and a number average molecular
weight (Mn) of 8,000 to 20,000 in view of the low-temperature
fixing properties and gloss stability of the toner.
Examples of the polymerizable monomer used for the styrene-acrylic
resin include aromatic vinyl monomers and (meth)acrylate monomers.
The polymerizable monomer preferably has a radically polymerizable
ethylenically unsaturated bond.
Examples of the aromatic vinyl monomers include styrene,
o-methylstyrene, m-methylstyrene, p-methylstyrene,
p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, p-ethylstyrene,
p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene,
p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene,
p-n-dodecylstyrene, 2,4-dimethylstyrene, 3,4-dichlorostyrene, and
derivatives thereof. These aromatic vinyl monomers may be used
alone or in combination.
Examples of the (meth)acrylate monomers include n-butyl acrylate,
methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl
acrylate, cyclohexyl acrylate, phenyl acrylate, methyl
methacrylate, ethyl methacrylate, butyl methacrylate, hexyl
methacrylate, 2-ethylhexyl methacrylate, .beta.-hydroxyethyl
acrylate, .gamma.-aminopropyl acrylate, stearyl methacrylate,
dimethylaminoethyl methacrylate, and diethylaminoethyl
methacrylate. These (meth)acrylate monomers may be used alone or in
combination. Preferred is a combination of a styrene monomer and an
acrylate or methacrylate monomer.
The polymerizable monomer may be a third vinyl monomer. Examples of
the third vinyl monomer include acid monomers, such as acrylic
acid, methacrylic acid, maleic anhydride, and vinylacetic acid,
acrylamide, methacrylamide, acrylonitrile, ethylene, propylene,
butylene, vinyl chloride, N-vinylpyrrolidone, and butadiene.
The polymerizable monomer may be a polyfunctional vinyl monomer.
Examples of the polyfunctional vinyl monomer include diacrylates of
ethylene glycol, propylene glycol, butylene glycol, and hexylene
glycol, divinylbenzene, and dimethacrylates and trimethacrylates of
tri- or higher-valent alcohols, such as pentaerythritol and
trimethylolpropane.
The styrene-acrylic resin according to the present invention is
preferably prepared by any known emulsion polymerization process.
According to the emulsion polymerization process, the
styrene-acrylic resin is prepared through polymerization of a
polymerizable monomer (e.g., styrene or acrylate) dispersed in an
aqueous medium described below. A surfactant is preferably used for
dispersion of the polymerizable monomer in an aqueous medium. A
polymerization initiator or a chain transfer agent may be used for
polymerization of the polymerizable monomer.
<Amorphous Polyester Resin>
The amorphous polyester resin exhibits a glass transition point
(T.sub.g) and no melting point (i.e., no clear endothermic peak
during temperature elevation) in an endothermic curve prepared by
differential scanning calorimetry (DSC).
If the amorphous polyester resin satisfies the aforementioned
definitions, the amorphous polyester resin may be derived from any
amorphous polyester resin or may include a styrene-acrylic modified
polyester resin described below.
The amorphous polyester resin is preferably an amorphous polyester
resin chemically bonded to a styrene-acrylic resin (hereinafter may
be referred to as "styrene-acrylic modified polyester resin") for
the following reason. The incorporation of the styrene-acrylic
resin into the main resin (amorphous resin; i.e., binder resin
other than crystalline resin) contained in the core particle leads
to high compatibility between the styrene-acrylic resin and the
main resin, resulting in improved releasability of the core-shell
toner during fixation, and high toner retention after fixation.
As used herein, the term "styrene-acrylic modified polyester resin"
refers to a resin (hybrid resin) having a polyester molecular
structure including an amorphous polyester chain (hereinafter may
be referred to as "polyester segment") molecularly bonded to the
aforementioned styrene-acrylic copolymer segment. Thus, the
styrene-acrylic modified polyester resin has a copolymeric
structure including the styrene-acrylic copolymer segment
molecularly bonded to the amorphous polyester segment.
The styrene-acrylic modified polyester resin serving as the
amorphous polyester resin is clearly distinguished from the hybrid
crystalline polyester resin as described below. Unlike the
crystalline polyester resin segment of the hybrid crystalline
polyester resin, the amorphous polyester segment of the amorphous
styrene-acrylic modified polyester resin is an amorphous molecular
chain having no clear melting point and a relatively high glass
transition temperature (T.sub.g). These properties can be confirmed
through differential scanning calorimetry (DSC) of the toner. The
monomer for the amorphous polyester segment has a chemical
structure different from that of the monomer for the crystalline
polyester resin segment, and thus these monomers can be
distinguished from each other by, for example, NMR analysis.
(Amorphous Polyester Segment)
The amorphous polyester segment is composed of a polyhydric alcohol
component and a polyvalent carboxylic acid component.
The polyhydric alcohol component may be of any type. The polyhydric
alcohol component is preferably an aromatic diol or a derivative
thereof in view of the charging properties and strength of the
toner. Examples of the aromatic diol and its derivative include
bisphenols, such as bisphenol A and bisphenol F; and alkylene oxide
adducts of bisphenols, such as ethylene oxide adducts and propylene
oxide adducts of bisphenols.
Among these polyhydric alcohol components, preferred are ethylene
oxide adducts and propylene oxide adducts of bisphenol A in view of
an improvement in charging uniformity. These polyhydric alcohol
components may be used alone or in combination.
The polyvalent carboxylic acid component condensed with the
polyhydric alcohol component may be of any type. Examples of the
polyvalent carboxylic acid component include aromatic carboxylic
acids, such as terephthalic acid, isophthalic acid, phthalic
anhydride, trimellitic anhydride, pyromellitic acid, and
naphthalenedicarboxylic acid; aliphatic carboxylic acids, such as
fumaric acid, maleic anhydride, succinic acid, adipic acid, sebacic
acid, and alkenylsuccinic acid; and lower alkyl esters and
anhydrides of these acids. These polyvalent carboxylic acid
components may be used alone or in combination.
The amorphous polyester resin preferably has a number average
molecular weight (Mn) of 2,000 to 10,000 in view of easy control of
the plasticity of the component.
The amorphous polyester segment may be prepared through any known
process. For example, the amorphous polyester segment can be
prepared through polycondensation (esterification) between the
aforementioned polyvalent carboxylic acid and polyhydric alcohol in
the presence of any known esterification catalyst.
(Esterification Catalyst)
Examples of the known esterification catalyst include compounds of
alkali metals, such as sodium and lithium; compounds containing
group 2 elements, such as magnesium and calcium; compounds of
metals, such as aluminum, zinc, manganese, antimony, titanium, tin,
zirconium, and germanium; phosphite compounds; phosphate compounds;
and amine compounds. Specific examples of the tin compound include
dibutyltin oxide, tin octylate, tin dioctylate, and salts thereof.
Examples of the titanium compound include titanium alkoxides, such
as tetra-n-butyl titanate, tetraisopropyl titanate, tetramethyl
titanate, and tetrastearyl titanate; titanium acylates, such as
polyhydroxytitanium stearate; and titanium chelate compounds, such
as titanium tetraacetylacetonate, titanium lactate, and titanium
triethanolaminate. Examples of the germanium compound include
germanium dioxide. Examples of the aluminum compounds include
oxides, such as poly(aluminum hydroxide); aluminum alkoxides; and
tributyl aluminate. These compounds may be used alone or in
combination.
(Styrene-Acrylic Polymer Segment)
The styrene-acrylic polymer segment is composed of an aromatic
vinyl monomer, a (meth)acrylate monomer, and a bireactive
monomer.
The aromatic vinyl monomer may be any of those described above in
the section <styrene-acrylic resin>.
These aromatic vinyl monomers may be used alone or in
combination.
The (meth)acrylate monomer may be any of those described above in
the section <styrene-acrylic resin>. These (meth)acrylate
monomers may be used alone or in combination.
The aromatic vinyl monomer or (meth)acrylate monomer used for
forming the styrene-acrylic polymer segment is preferably styrene
or its derivative in view of achievement of superior charging
properties and high image quality. In detail, the amount of styrene
or its derivative is preferably 50 mass % or more relative to the
total amount of the monomers (aromatic vinyl monomer and
(meth)acrylate monomer) used for forming the styrene-acrylic
polymer segment.
The bireactive monomer may be of any type having a polymerizable
unsaturated group and a group that can react with the polyvalent
carboxylic acid monomer and/or the polyhydric alcohol monomer for
forming the amorphous polyester segment. Specific examples of the
bireactive monomer include acrylic acid, methacrylic acid, fumaric
acid, maleic acid, and maleic anhydride. In the present invention,
the bireactive monomer is preferably acrylic acid or methacrylic
acid.
(Resin Usable in Combination with Styrene-Acrylic Modified
Polyester Resin)
If the amorphous resin A or the amorphous resin B is a
styrene-acrylic modified polyester resin, an additional resin may
be used in combination with the styrene-acrylic modified polyester
resin so long as the advantageous effects of the present invention
are not inhibited. Examples of the additional resin include
styrene-acrylic resins, polyester resins, and urethane resins.
The amount of the styrene-acrylic modified polyester resin
contained in the shell is preferably 70 to 100 mass %, more
preferably 90 to 100 mass %, relative to the total amount (100 mass
%) of the resins forming the shell.
A styrene-acrylic modified polyester resin content of the shell of
70 mass % or more leads to sufficient compatibility between the
core particle and the shell. This configuration contributes to
formation of a desired shell and prevents unsatisfactory thermal
resistance during storage, charging properties, and fracture
resistance.
(Styrene-Acrylic Content)
If the amorphous resin B is a styrene-acrylic modified polyester
resin and the amorphous resin A is a styrene-acrylic resin or the
amorphous resin A is a styrene-acrylic modified polyester resin and
the amorphous resin B is a styrene-acrylic resin, the amount of the
styrene-acrylic polymer segment contained in the styrene-acrylic
modified polyester resin (as used herein, the amount refers to as
"styrene-acrylic content") is preferably 5 to 30 mass %, more
preferably 10 to 25 mass %. A styrene-acrylic content falling
within the above range leads to high compatibility of the
styrene-acrylic modified polyester resin with the styrene-acrylic
resin contained in the core particle, resulting in improved
releasability of the core-shell toner during fixation, and high
toner retention after fixation.
In specific, the styrene-acrylic content corresponds to the
proportion of the total mass of the aromatic vinyl monomer and the
(meth)acrylate monomer to the total mass of the materials used for
the synthesis of the styrene-acrylic modified polyester resin;
i.e., the total mass of the monomer for the unmodified polyester
resin (to form the amorphous polyester segment), the aromatic vinyl
monomer and (meth)acrylate monomer for the styrene-acrylic polymer
segment, and the bireactive monomer for bonding these segments.
A styrene-acrylic content falling within the above range leads to
appropriate control of the compatibility between the
styrene-acrylic modified polyester resin and the styrene-acrylic
resin. This contributes to appropriate balance between the
following two types of fusions; i.e., the fusion of the interface
between the styrene-acrylic modified polyester resin and the
styrene-acrylic resin, and the fusion of the styrene-acrylic
modified polyester resin.
If the amorphous resin B is a styrene-acrylic modified polyester
resin and the amorphous resin A is a styrene-acrylic resin, the
resultant shell coat or coat domain exhibits superior thermal
resistance and fixing properties, and the toner matrix particles
have smooth surfaces. A styrene-acrylic content of 5 mass % or more
leads to appropriate formation of the shell membrane or membranous
domain, resulting in sufficient fusion of the interface between the
styrene-acrylic modified polyester resin and the core particle.
This prevents insufficient fusion of the toner during fixation.
Thus, the styrene-acrylic content is preferably 5 mass % or more in
view of satisfactory low-temperature fixing properties and document
offset resistance. The styrene-acrylic content is also preferably
30 mass % or less in view of prevention of an excessive increase in
the softening point of the styrene-acrylic modified polyester resin
and achievement of satisfactory low-temperature fixing properties
of the toner particles.
(Bonding Between Styrene-Acrylic Polymer Segment and Polyester
Segment)
The styrene-acrylic polymer segment may be bonded to the end of the
polyester main chain, or may be in the form of a side chain grafted
to the polyester main chain. The styrene-acrylic modified polyester
resin prepared through bonding of the styrene-acrylic polymer
segment to the end of the polyester resin chain is likely to form
domains of the polyester segment and the styrene-acrylic polymer
segment. Thus, the amorphous polyester segment is readily oriented
to the toner surface layer during the coagulation--fusion process,
and the styrene-acrylic polymer segment is readily oriented to the
toner surface layer in the case where the core particle contains
the styrene-acrylic resin, resulting in formation of a dense
core-shell structure.
(Preparation of Styrene-Acrylic Modified Polyester Resin)
The styrene-acrylic modified polyester resin may be prepared by any
common process. Among the following four typical processes, process
(A) is most preferred.
(A) Process involving preliminary polymerization of an amorphous
polyester segment, reaction of the amorphous polyester segment with
a bireactive monomer, and reaction of the resultant product with an
aromatic vinyl monomer and a (meth)acrylate monomer for formation
of a styrene-acrylic polymer segment. (B) Process involving
preliminary polymerization of a styrene-acrylic polymer segment,
reaction of the styrene-acrylic polymer segment with a bireactive
monomer, and reaction of the resultant product with a polyvalent
carboxylic acid monomer and a polyhydric alcohol monomer for
formation of an amorphous polyester segment. (C) Process involving
preliminary polymerization of an amorphous polyester segment and a
styrene-acrylic polymer segment, and bonding of these segments
through reaction of the segments with a bireactive monomer. (D)
Process involving preliminary polymerization of an amorphous
polyester segment, and addition polymerization of a styrene-acrylic
polymerizable monomer with a polymerizable unsaturated group of the
amorphous polyester segment for bonding of the monomer and the
segment.
In specific, process (A) involves, for example, the following
steps:
(1) mixing of an unmodified polyester resin with an aromatic vinyl
monomer, a (meth)acrylate monomer, and a bireactive monomer;
and
(2) polymerization of the aromatic vinyl monomer and the
(meth)acrylate monomer.
This process can bond an amorphous polyester segment to a
styrene-acrylic polymer segment.
Through the mixing Step (1) and the polymerization Step (2), the
hydroxy group at the end of the amorphous polyester segment forms
an ester bond with the carboxy group of the bireactive monomer, and
the vinyl group of the bireactive monomer is bonded to the vinyl
group of the aromatic vinyl monomer or the (meth)acrylic monomer to
form a styrene-acrylic polymer segment.
The mixing Step (1) preferably involves heating. The heating
temperature may be any temperature that allows for the mixing of
the unmodified polyester resin, the aromatic vinyl monomer, the
(meth)acrylate monomer, and the bireactive monomer. The heating
temperature is preferably 80 to 120.degree. C., more preferably 85
to 115.degree. C., still more preferably 90 to 110.degree. C., in
view of effective mixing and easy control of polymerization.
The total amount of the aromatic vinyl monomer and the
(meth)acrylate monomer is preferably 5 to 30 mass %, particularly
preferably 5 to 20 mass %, relative to the total amount (100 mass
%) of the resin materials used for the preparation of the
styrene-acrylic modified polyester resin; i.e., the total amount of
the unmodified polyester resin, the aromatic vinyl monomer, the
(meth)acrylate monomer, and the bireactive monomer.
It is preferred that the proportion of the total mass of the
aromatic vinyl monomer and the (meth)acrylate monomer to the total
mass of the resin materials falls within the above range. A
proportion falling within the range leads to appropriate control of
the compatibility between the styrene-acrylic modified polyester
resin and the core particle and formation of a desired shell,
resulting in improved releasability of the toner during fixation,
and high toner retention after fixation.
A proportion of 5 mass % or more leads to formation of a desired
shell from the styrene-acrylic modified polyester resin and
prevention of excessive exposure of the core particle, resulting in
sufficient thermal resistance during storage and charging
properties of the toner.
A proportion of 30 mass % or less leads to prevention of an
excessive increase in the softening point of the styrene-acrylic
modified polyester resin, resulting in satisfactory low-temperature
fixing properties of the toner.
The amount of the bireactive monomer is preferably 0.1 to 10.0 mass
%, particularly preferably 0.5 to 3.0 mass %, relative to the total
amount (100 mass %) of the resin materials used for the preparation
of the styrene-acrylic modified polyester resin; i.e., the total
amount of the unmodified polyester resin, the aromatic vinyl
monomer, the (meth)acrylate monomer, and the bireactive
monomer.
[Crystalline Material]
The core particle according to the present invention contains a
crystalline material.
The crystalline material exhibits a clear endothermic peak, rather
than a stepwise endothermic change, in differential scanning
calorimetry (DSC) of the toner. The clear endothermic peak has a
half width of 15.degree. C. or less as determined by DSC described
in Examples at a heating rate of 10.degree. C./min.
Specific examples of the crystalline material include crystalline
polyester resins, and release agents, such as waxes.
The crystalline material according to the present invention
preferably includes a crystalline resin or a release agent selected
from a hydrocarbon wax and an ester wax, and the crystalline
material preferably has a melting point (T.sub.m-c) equal to or
higher than (the glass transition temperature (T.sub.g-b) of the
amorphous resin B+3).degree. C., in view of a further improvement
in thermal resistance during storage and transfer efficiency. If
the crystalline material has a melting point (T.sub.m-c) equal to
or higher than (the glass transition temperature (T.sub.g-b) of the
amorphous resin B+3).degree. C., coalescence and enlargement of
crystalline material grains is prevented during addition of the
amorphous resin B or coagulation of the core particle with the
shell particle, leading to avoidance of bleeding out of the
crystalline material to the surface layer of the core particle. As
a result, low thermal resistance during storage and low transfer
efficiency of the toner can be prevented.
The crystalline material has a melting point (T.sub.m-c) of
preferably 66 to 85.degree. C., more preferably 68 to 78.degree. C.
A melting point (T.sub.m-c) falling within this range probably
contributes to high compatibility between thermal resistance and
plasticity/releasability during fixation.
The crystalline resin may be of any type, such as a crystalline
polyester resin.
<Crystalline Polyester Resin>
The crystalline polyester resin is derived from any known polyester
resin prepared through polycondensation between a di- or
higher-valent carboxylic acid (polyvalent carboxylic acid) and a
di- or higher-valent alcohol (polyhydric alcohol). As described
above, the crystalline polyester resin exhibits a clear endothermic
peak, rather than a stepwise endothermic change, by differential
scanning calorimetry (DSC) of the toner.
The crystalline polyester resin preferably satisfies Expression
(A): 5.ltoreq.|C.sub.acid-C.sub.alcohol|.ltoreq.12 Expression (A):
where C.sub.alcohol represents the number of carbon atoms of the
main chain of a structural unit derived from a polyhydric alcohol
forming the crystalline polyester resin and C.sub.acid represents
the number of carbon atoms of the main chain of a structural unit
derived from a polyvalent carboxylic acid forming the crystalline
polyester resin.
Each toner matrix particle includes a crystalline polyester resin
having alkyl chains of different lengths that are repeated via
ester bonds. This configuration prevents coagulation of grains of
the crystalline polyester resin and thus formation of large crystal
domains of the crystalline polyester resin even in high-temperature
environments. Thus, the toner maintains fixing properties even
after being stored at high temperatures.
From the viewpoint of effective achievement of similar advantageous
effects, the crystalline polyester resin preferably satisfies
Expression (B): 6.ltoreq.|C.sub.acid-C.sub.alcohol|.ltoreq.10.
Expression(B):
From the viewpoint of an improvement in fixing properties, the
crystalline polyester resin preferably satisfies Expression (C):
C.sub.alcohol<C.sub.acid Expression (C):
From the viewpoint of an improvement in fixing properties, the
number of carbon atoms of the main chain of the structural unit
derived from the polyhydric alcohol forming the crystalline
polyester resin (i.e., C.sub.alcohol) is preferably 2 to 12, and
the number of carbon atoms of the main chain of the structural unit
derived from the polyvalent carboxylic acid forming the crystalline
polyester resin (i.e., C.sub.acid) is preferably 6 to 16.
The crystalline polyester resin satisfying the aforementioned
definitions may be in any form.
A dicarboxylic acid component is used as the polyvalent carboxylic
acid component. The dicarboxylic acid component is preferably an
aliphatic dicarboxylic acid, and may be used in combination with an
aromatic dicarboxylic acid. The aliphatic dicarboxylic acid is
preferably a linear-chain aliphatic dicarboxylic acid. The use of a
linear-chain aliphatic dicarboxylic acid is advantageous in view of
an improvement in crystallinity. Two or more dicarboxylic acid
components may be used in combination.
Examples of the aliphatic dicarboxylic acid include oxalic acid,
malonic acid, succinic acid, glutaric acid, adipic acid, pimelic
acid, suberic acid, azelaic acid, sebacic acid,
1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid,
1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid
(dodecanedioic acid), 1,13-tridecanedicarboxylic acid,
1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic
acid, and 1,18-octadecanedicarboxylic acid. Lower alkyl esters and
anhydrides of these acids may also be used.
Among the aforementioned aliphatic dicarboxylic acids, preferred
are aliphatic dicarboxylic acids having 6 to 14 carbon atoms in
view of the advantageous effects of the present invention.
Examples of the aromatic dicarboxylic acid that can be used in
combination with the aliphatic dicarboxylic acid include
terephthalic acid, isophthalic acid, o-phthalic acid,
t-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid, and
4,4'-biphenyldicarboxylic acid. Among these acids, preferred are
terephthalic acid, isophthalic acid, and t-butylisophthalic acid,
which can be readily available and emulsified.
The dicarboxylic acid component of the crystalline polyester resin
contains an aliphatic dicarboxylic acid in an amount of preferably
50 mol % or more, more preferably 70 mol % or more, still more
preferably 80 mol % or more, particularly preferably 100 mol %. An
aliphatic dicarboxylic acid content of the dicarboxylic acid
component of 50 mol % or more leads to sufficient crystallinity of
the crystalline polyester resin.
A diol component is used as the polyhydric alcohol component. The
diol component is preferably an aliphatic diol. The diol component
may optionally contain any diol other than an aliphatic diol. The
aliphatic diol is preferably a linear-chain aliphatic diol. The use
of a linear-chain aliphatic diol is advantageous in view of an
improvement in crystallinity. Two or more diol components may be
used in combination.
Examples of the aliphatic diol include ethylene glycol,
1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol,
1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol,
1,14-tetradecanediol, 1,18-octadecandiol, and
1,20-eicosanediol.
Among the aforementioned aliphatic diols, preferred are aliphatic
diols having 2 to 12 carbon atoms in view of the advantageous
effects of the present invention. More preferred are aliphatic
diols having 4 to 12 carbon atoms.
Examples of the optional diol other than the aliphatic diol include
diols having a double bond, diols having a sulfonate group, and
diols having a bisphenol structure. Specific examples of the diols
having a double bond include 2-butene-1,4-diol, 3-butene-1,6-diol,
and 4-butene-1,8-diol.
The diol component of the crystalline polyester resin contains an
aliphatic diol in an amount of preferably 50 mol % or more, more
preferably 70 mol % or more, still more preferably 80 mol % or
more, particularly preferably 100 mol %. An aliphatic diol content
of the diol component of 50 mol % or more leads to sufficient
crystallinity of the crystalline polyester resin, resulting in
superior low-temperature fixing properties of the resultant toner,
and glossy images provided by the toner.
The stoichiometric ratio of the hydroxy group [OH] of the diol
component to the carboxy group [COOH] of the dicarboxylic acid
component ([OH]/[COOH]) is preferably 2.0/1.0 to 1.0/2.0, more
preferably 1.5/1.0 to 1.0/1.5, particularly preferably 1.3/1.0 to
1.0/1.3.
The crystalline polyester resin may be prepared through any known
process. For example, the crystalline polyester resin can be
prepared through polycondensation (esterification) between the
aforementioned polyvalent carboxylic acid and polyhydric alcohol in
the presence of any known esterification catalyst.
The polymerization may be performed at any temperature. The
polymerization temperature is preferably 150 to 250.degree. C. The
polymerization may be performed for any period of time. The
polymerization time is preferably 0.5 to 10 hours. The
polymerization may optionally be performed in a reaction system at
reduced pressure.
If the crystalline polyester resin satisfies the aforementioned
definitions, the crystalline polyester resin may be derived from
any crystalline polyester resin or may include a hybrid crystalline
polyester resin described below. The hybrid crystalline polyester
resin will now be briefly described.
<Hybrid Crystalline Polyester Resin>
The hybrid crystalline polyester resin is a chemically bonded
composite of a crystalline polyester resin segment and an amorphous
resin segment other than the polyester resin.
The crystalline polyester resin segment is derived from any
crystalline polyester resin. Thus, the crystalline polyester resin
segment refers to a molecular chain having the same chemical
structure as the crystalline polyester resin. The amorphous resin
segment other than the polyester resin is derived from any
amorphous resin other than the polyester resin. Thus, the amorphous
resin segment refers to a molecular chain having the same chemical
structure as the amorphous resin other than the polyester
resin.
(Crystalline Polyester Resin Segment)
The crystalline polyester resin segment is derived from the
aforementioned crystalline polyester resin, and exhibits a clear
endothermic peak, rather than a stepwise endothermic change, by
differential scanning calorimetry (DSC) of the toner.
The crystalline polyester resin segment satisfying the
aforementioned definitions may be in any form. For example, the
following copolymer resins correspond to the hybrid crystalline
polyester resin according to the present invention: a resin
composed of a crystalline polyester resin segment having a main
chain copolymerized with any other component and a resin composed
of a crystalline polyester resin segment copolymerized with the
main chain of any other component, with the proviso that the toner
containing such a copolymer resin exhibits the aforementioned clear
endothermic peak.
The crystalline polyester resin segment may be prepared through any
known process. For example, the segment can be prepared through
polycondensation (esterification) between the aforementioned
polyvalent carboxylic acid and polyhydric alcohol in the presence
of any known esterification catalyst.
The crystalline polyester resin segment is preferably prepared
through polycondensation of the aforementioned polyvalent
carboxylic acid and polyhydric alcohol and a compound that
chemically bonds to the amorphous resin segment.
The hybrid crystalline polyester resin contains the aforementioned
crystalline polyester resin segment and the below-described
amorphous resin segment other than polyester resin.
(Amorphous Resin Segment Other than Polyester Resin)
The amorphous resin segment other than the polyester resin
(hereinafter may be referred to simply as "amorphous resin
segment") is a segment for controlling the compatibility between
the amorphous resin and the hybrid crystalline polyester resin. The
presence of the amorphous resin segment can improve the
compatibility between the hybrid crystalline polyester resin and
the amorphous resin to facilitate merging of the hybrid crystalline
polyester resin into the amorphous resin, resulting in improved
charging uniformity.
The amorphous resin segment is derived from an amorphous resin
other than the crystalline polyester resin. The amorphous resin
segment contained in the hybrid crystalline polyester resin (and in
the toner) can be confirmed through identification of the chemical
structure by, for example, NMR or methylation P-GC/MS.
The results of differential scanning calorimetry (DSC) performed on
a resin having the same chemical structure and molecular weight as
those of the amorphous resin segment show that the resin has no
melting point but has a relatively high glass transition
temperature (T.sub.g). In the DSC of the resin having the same
chemical structure and same molecular weight as those of the
amorphous resin segment, the glass transition temperature
(T.sub.g1) in the first heating process is preferably 30 to
80.degree. C., particularly preferably 40 to 65.degree. C.
The amorphous resin segment satisfying the aforementioned
definitions may be in any form. For example, the following
copolymer resins correspond to the hybrid crystalline polyester
resin containing the amorphous resin segment according to the
present invention: a resin composed of an amorphous resin segment
having a main chain copolymerized with any other component and a
resin composed of an amorphous resin segment copolymerized with the
main chain of any other component, with the proviso that the toner
containing such a copolymer has the aforementioned amorphous resin
segment.
The amorphous resin segment is preferably composed of a resin
similar to the amorphous resin A. Such an amorphous resin segment
significantly enhances the compatibility between the hybrid
crystalline polyester resin and the amorphous resin. Thus, the
hybrid crystalline polyester resin is more readily incorporated
into the amorphous resin, resulting in further improved charging
uniformity.
The amorphous resin segment may be composed of any resin component.
Examples of the resin component include vinyl resins, urethane
resins, and urea resins. Among these resins, preferred are vinyl
resins in view of easy control of thermoplastic
characteristics.
The vinyl resin may be of any type that is prepared through
polymerization of a vinyl compound. Examples of the vinyl resin
include acrylate resins, styrene-acrylate resins, and
ethylene-vinyl acetate resins. These vinyl resins may be used alone
or in combination.
Among these vinyl resins, preferred are styrene-acrylate resins
(styrene-acrylic resins) in view of plasticity during thermal
fixation. Thus, the styrene-acrylic polymer segment serving as the
amorphous resin segment will be described below.
The styrene-acrylic polymer segment is prepared through addition
polymerization of at least a styrene monomer and a (meth)acrylate
monomer. As used herein, the "styrene monomer" includes styrene,
which is represented by the formula
CH.sub.2.dbd.CH--C.sub.6H.sub.5, and styrene derivatives having
known side chains or functional groups in the styrene structure. As
used herein, the "(meth)acrylate monomer" includes acrylate and
methacrylate compounds represented by the formula
CH.sub.2.dbd.CHCOOR (where R is an alkyl group), and ester
compounds having known side chains or functional groups in the
structure of acrylate or methacrylate derivatives.
Preferred examples of the styrene monomers and the (meth)acrylate
monomers that can form the styrene-acrylic copolymer segment
include aromatic vinyl monomers and (meth)acrylate monomers
described in the section <styrene-acrylic resin>. Other
styrene monomers and (meth)acrylate monomers may be used in the
present invention for formation of the styrene-acrylic copolymer
segment.
The content of the amorphous resin segment is preferably 2 to 20
mass %, more preferably 4 to 15 mass %, still more preferably 5 to
11 mass %, relative to the entire amount of the hybrid crystalline
polyester resin. A content of the amorphous resin segment within
the above range leads to sufficient crystallinity of the hybrid
crystalline polyester resin.
(Preparation of Hybrid Crystalline Polyester Resin)
The hybrid resin according to the present invention may be prepared
by any process that can produce a polymer having a structure
composed of the crystalline polyester resin segment and the
amorphous resin segment molecularly bonded thereto. For example,
the hybrid resin may be prepared in the same manner as described
above in the section <preparation of styrene-acrylic modified
polyester resin> except that the amorphous polyester segment is
replaced with the crystalline polyester resin segment. In this
case, the styrene-acrylic polymer segment may be replaced with
another amorphous resin segment.
<Release Agent (Wax)>
Any known release agent may be used in the present invention.
Examples of the release agent include polyolefin waxes, such as
polyethylene wax and polypropylene wax; branched-chain hydrocarbon
waxes, such as microcrystalline wax; hydrocarbon waxes, such as
paraffin wax and Sasolwax; dialkyl ketone waxes, such as distearyl
ketone; ester waxes, such as carnauba wax, montan wax, behenyl
behenate, trimethylolpropane tribehenate, pentaerythritol
tetrabehenate, pentaerythritol diacetate dibehenate, glycerin
tribehenate, 1,18-octadecanediol distearate, tristearyl
trimellitate, and distearyl maleate; and amide waxes, such as
ethylenediaminebehenylamide and trimellitic acid tristearylamide.
These release agents may be used alone or in combination.
The release agent has a melting point of preferably 40 to
160.degree. C., more preferably 50 to 120.degree. C., still more
preferably 60 to 90.degree. C. A melting point of the release agent
within the above range leads to sufficient thermal resistance
during storage of the toner. In addition, toner images can be
reliably formed during fixation at a low temperature without
causing cold offset. The release agent content of the toner is
preferably 1 to 30 mass %, more preferably 5 to 20 mass %.
<Colorant>
The colorant according to the present invention may be of any type,
such as carbon black, a magnetic material, a dye, or a pigment.
Examples of the carbon black include channel black, furnace black,
acetylene black, thermal black, and lamp black. Examples of the
magnetic material include ferromagnetic metals, such as iron,
nickel, and cobalt; alloys of these metals; ferromagnetic metal
compounds, such as ferrite and magnetite; alloys containing no
ferromagnetic metal and exhibiting ferromagnetism through thermal
treatment, such as Heusler alloys (e.g., manganese-copper-aluminum
and manganese-copper-tin); and chromium dioxide.
Examples of the black colorant include carbon black materials, such
as furnace black, channel black, acetylene black, thermal black,
and lamp black; and powdery magnetic materials, such as magnetite
and ferrite.
Examples of the magenta or red colorant include C. I. Pigment Reds
2, 3, 5, 6, 7, 15, 16, 48:1, 53:1, 57:1, 60, 63, 64, 68, 81, 83,
87, 88, 89, 90, 112, 114, 122, 123, 139, 144, 149, 150, 163, 166,
170, 177, 178, 184, 202, 206, 207, 209, 222, 238, and 269.
Examples of the orange or yellow colorant include C. I. Pigment
Oranges 31 and 43, and C. I. Pigment Yellows 12, 14, 15, 17, 74,
83, 93, 94, 138, 155, 162, 180, and 185.
Examples of the green or cyan colorant include C. I. Pigment Blues
2, 3, 15, 15:2, 15:3, 15:4, 16, 17, 60, 62, and 66, and C. I.
Pigment Green 7.
These colorants may be used alone or in combination.
The content of the colorant is preferably 1 to 30 mass %, more
preferably 2 to 20 mass %, relative to the entire amount of the
toner. The toner may contain any mixture of the aforementioned
colorants. A content of the colorant within such a range leads to
satisfactory color reproduction of images.
The colorant has a volume average particle size of 10 to 1,000 nm,
preferably 50 to 500 nm, more preferably 80 to 300 nm.
[Additional Component]
The toner matrix particles according to the present invention may
optionally contain an internal additive (e.g., a charge controlling
agent) or an external additive (e.g., inorganic microparticles,
organic microparticles, or a lubricant) in addition to the
aforementioned components.
<Charge Controlling Agent>
The charge controlling agent may be any known compound. Examples of
such a compound include nigrosine dyes, metal salts of naphthenic
acid and higher fatty acids, alkoxylated amines, quaternary
ammonium salts, azo-metal complexes, and salicylic acid metal
salts.
The content of the charge controlling agent is typically 0.1 to 10
mass %, preferably 0.5 to 5 mass %, relative to the entire amount
(100 mass %) of the binder resin contained in the resultant toner
matrix particles.
The charge controlling agent has a number average primary particle
size of, for example, 10 to 1,000 nm, preferably 50 to 500 nm, more
preferably 80 to 300 nm.
(External Additive)
The toner may contain any known external additive in view of
improvements in charging properties, fluidity, and cleanability.
Examples of the additive include inorganic microparticles, organic
microparticles, and lubricants. Such an external additive may be
deposited onto the surfaces of the toner matrix particles.
The inorganic microparticles are preferably composed of, for
example, silica, titania, alumina, or strontium titanate.
The inorganic microparticles may optionally be subjected to
hydrophobic treatment.
The organic microparticles may be spherical organic microparticles
having a number average primary particle size of about 10 to 2,000
nm. In detail, the organic microparticles may be composed of a
homopolymer of styrene or methyl methacrylate or a copolymer of
these monomers.
The lubricant is used for further improving the cleanability and
transfer efficiency of the toner. Examples of the lubricant include
metal salts of higher fatty acids, such as zinc, aluminum, copper,
magnesium, and calcium salts of stearic acid, zinc, manganese,
iron, copper, and magnesium salts of oleic acid, zinc, copper,
magnesium, and calcium salts of palmitic acid, zinc and calcium
salts of linoleic acid, and zinc and calcium salts of ricinoleic
acid. These external additives may be used in combination.
The content of the external additive is preferably 0.1 to 10.0 mass
% relative to the entire amount (100 mass %) of the toner matrix
particles.
The external additive may be mixed with the toner matrix particles
with any known mixer, such as a Turbula mixer, a Henschel mixer, a
Nauta mixer, or a V-type mixer.
<<Steps I to III>>
Now will be described Steps I to III of the method of producing a
toner for developing electrostatic images of the present invention.
In the embodiment described below, Step III is followed by
additional steps; i.e., a heating-cooling step and a
separation-drying step. The method of the present invention may
include other additional steps.
[Step I]
Step I involves dispersing at least the amorphous resin A and the
crystalline material in an aqueous medium to prepare a dispersion,
and adjusting the temperature of the dispersion to be equal to or
higher than (the glass transition temperature (T.sub.g-a) of the
amorphous resin A+10).degree. C. and equal to or lower than (the
melting point (T.sub.m-c) of the crystalline material+10).degree.
C., to prepare a core particle dispersion through coagulation and
coalescence of at least the amorphous resin A and the crystalline
material.
The temperature of the dispersion containing the amorphous resin A
and the crystalline material is preferably adjusted to be equal to
or higher than (the glass transition temperature (T.sub.g-a) of the
amorphous resin A+15).degree. C. and equal to or lower than (the
melting point (T.sub.m-c) of the crystalline material+8).degree.
C., more preferably a temperature equal to or higher than
(T.sub.g-a+20).degree. C. and equal to or lower than
(T.sub.m-c)+7).degree. C.
A temperature adjusted to be equal to or higher than (the glass
transition temperature (T.sub.g-a) of the amorphous resin
A+15).degree. C. leads to a decrease in viscosity of the amorphous
resin A (i.e., activation of molecular motion), resulting in a
reduced number of irregularities of core particles. A temperature
adjusted to be equal to or lower than (the melting point
(T.sub.m-c) of the crystalline material+8).degree. C. prevents
excessive mixing of the crystalline material, resulting in
satisfactory releasability and plasticity. This adjustment also
contributes to improvements in dispersion of a colorant, the
charging properties of the toner, and the quality of images.
The dispersion containing the amorphous resin A and the crystalline
material is preferably prepared through mixing of a dispersion
containing particles of the amorphous resin A (hereinafter may be
referred to as "amorphous resin A particle dispersion"), a
dispersion of the crystalline material (e.g., release agent or
crystalline resin), and a dispersion of the colorant in an aqueous
medium.
The coagulation and coalescence process preferably involves
addition of a coagulant to the dispersion containing the amorphous
resin A and the crystalline material. If the crystalline material
is the crystalline polyester resin, the addition of the crystalline
polyester resin is preferably preceded by the addition of the
coagulant.
If the amorphous resin A contains a release agent as the
crystalline material, the mixing of the crystalline material
dispersion may be omitted.
For incorporation of an internal additive (e.g., a release agent)
into the toner matrix particles, the internal additive may be
incorporated in the amorphous resin A particles. Alternatively, a
dispersion of internal additive microparticles may be separately
prepared, and the dispersion may be added before or after the
addition of the coagulant. In the case of incorporation of the
crystalline polyester resin, the internal additive microparticle
dispersion is preferably added before completion of the addition of
the crystalline polyester resin.
Now will be described the preparation of an amorphous resin A
particle dispersion, a colorant dispersion, and a crystalline
material dispersion.
In the following description, the amorphous resin A is a
styrene-acrylic resin, and the crystalline material is a release
agent.
(Preparation of Styrene-Acrylic Resin Particle Dispersion)
The styrene-acrylic resin (amorphous resin A) particle dispersion
is prepared through synthesis of a styrene-acrylic resin and then
dispersion of the styrene-acrylic resin in the form of
microparticles in an aqueous medium.
As described above, the styrene-acrylic resin may be synthesized by
any known emulsion polymerization process. For incorporation of a
release agent into styrene-acrylic resin particles, the release
agent is added during the polymerization of the styrene-acrylic
resin. In this case, the styrene-acrylic resin is preferably
prepared by a miniemulsion polymerization process.
The styrene-acrylic resin is dispersed in an aqueous medium by, for
example, process (i) or (ii) described below. Process (i) involves
formation of styrene-acrylic resin particles from a monomer for the
styrene-acrylic resin, and preparation of an aqueous dispersion of
the styrene-acrylic resin particles. Process (ii) involves
dissolution or dispersion of the styrene-acrylic resin in an
organic solvent to prepare an oil-phase solution, dispersion of the
oil-phase solution in an aqueous medium through phase inversion
emulsification to form oil droplets having a desired size, and
removal of the organic solvent.
As used herein, the term "aqueous medium" refers to a medium
containing water in an amount of 50 mass % or more. Examples of the
component of the aqueous medium other than water include organic
solvents miscible with water, such as methanol, ethanol,
2-propanol, butanol, acetone, methyl ethyl ketone,
dimethylformamide, methyl cellosolve, and tetrahydrofuran. Among
these organic compounds, preferred are alcohol solvents, such as
methanol, ethanol, 2-propanol, and butanol, which cannot dissolve
the resin. The aqueous medium preferably consists of water (e.g.,
deionized water).
Process (i) preferably involves addition of a monomer for the
styrene-acrylic resin to an aqueous medium together with a
polymerization initiator to prepare base particles through
polymerization, and then addition of a radically polymerizable
monomer for the styrene-acrylic resin and a polymerization
initiator to a dispersion of the base particles for seed
polymerization of the monomer with the base particles.
The polymerization initiator may be a water-soluble polymerization
initiator. Preferred examples of the water-soluble polymerization
initiator include water-soluble radical polymerization initiators,
such as potassium persulfate and ammonium persulfate.
The seed polymerization system for preparation of the
styrene-acrylic resin particles may involve the use of the
aforementioned chain transfer agent for controlling the molecular
weight of the styrene-acrylic resin. The chain transfer agent is
preferably mixed with the resin materials in the aforementioned
mixing step.
Process (ii) preferably involves the use of an organic solvent
having a low boiling point and low solubility in water for
preparation of the oil-phase solution in view of easy removal of
the solvent after formation of oil droplets. Specific examples of
the organic solvent include methyl acetate, ethyl acetate, methyl
ethyl ketone, isopropyl alcohol, methyl isobutyl ketone, toluene,
and xylene. These organic solvents may be used alone or in
combination.
The amount of an organic solvent (or the total amount of two or
more organic solvents) is typically 10 to 500 parts by mass,
preferably 100 to 450 parts by mass, more preferably 200 to 400
parts by mass, relative to 100 parts by mass of the styrene-acrylic
resin.
The amount of the aqueous medium is preferably 50 to 2,000 parts by
mass, more preferably 100 to 1,000 parts by mass, relative to 100
parts by mass of the oil-phase solution. An amount within the above
range leads to formation of oil droplets having a desired size
through effective emulsification and dispersion of the oil-phase
solution in the aqueous medium.
The aqueous medium may contain a dispersion stabilizer.
Alternatively, the aqueous medium may contain a surfactant or a
microparticulate resin for improving the dispersion stability of
oil droplets.
The dispersion stabilizer may be of any known type. The dispersion
stabilizer is preferably of an acid- or alkali-soluble type, such
as tricalcium phosphate, or an enzyme-degradable type from the
environmental viewpoint.
Examples of the surfactant include known anionic surfactants,
cationic surfactants, nonionic surfactants, and amphoteric
surfactants.
Examples of the microparticulate resin for improving the dispersion
stability include microparticulate poly(methyl methacrylate)
resins, microparticulate polystyrene resins, and microparticulate
poly(styrene-acrylonitrile) resins.
The oil-phase solution can be emulsified by use of mechanical
energy with any disperser. Examples of the disperser include
homogenizers, low-rate shearing dispersers, high-rate shearing
dispersers, frictional dispersers, high-pressure jet dispersers,
ultrasonic dispersers, and high-pressure impact dispersers (e.g.,
Ultimizer).
After the formation of the oil droplets, the entire dispersion of
the styrene-acrylic resin particles in the aqueous medium is
gradually heated under agitation and then maintained at a
predetermined temperature under vigorous agitation, followed by
removal of the organic solvent. The organic solvent may be removed
with, for example, an evaporator at reduced pressure.
The styrene-acrylic resin particles (oil droplets) in the
styrene-acrylic resin particle dispersion prepared by process (i)
or (ii) have a volume median particle size of preferably 60 to
1,000 nm, more preferably 80 to 500 nm. The volume median particle
size of the oil droplets can be adjusted by, for example, control
of the mechanical energy during emulsification and dispersion.
The content of the styrene-acrylic resin particles in the
styrene-acrylic resin particle dispersion is preferably 5 to 50
mass %, more preferably 10 to 30 mass %. A content of the
styrene-acrylic resin particles within the above range leads to a
narrow particles size distribution and an improvement in properties
of the toner.
(Preparation of Colorant Dispersion)
The colorant dispersion is prepared through dispersion of a
colorant in the form of microparticles in an aqueous medium.
The aqueous medium is as described above in the section
"preparation of styrene-acrylic resin particle dispersion." The
aqueous medium may contain a surfactant or resin microparticles for
improving the dispersion stability of the colorant.
The colorant may be dispersed in the aqueous medium by mechanical
energy with any disperser. The disperser may be the same as
described above in the section "preparation of styrene-acrylic
resin particle dispersion."
The content of the colorant microparticles in the colorant
dispersion is preferably 10 to 50 mass %, more preferably 15 to 40
mass %. A content of the colorant microparticles within the above
range leads to satisfactory color reproduction of images.
(Preparation of Release Agent Dispersion)
The release agent (crystalline material) dispersion is prepared
through dispersion of a release agent in the form of microparticles
in an aqueous medium.
The aqueous medium is as described above in the section
"preparation of styrene-acrylic resin particle dispersion." The
aqueous medium may contain a surfactant or resin microparticles for
improving the dispersion stability of the release agent.
The release agent may be dispersed in the aqueous medium by
mechanical energy with any disperser. The disperser may be the same
as described above in the section "preparation of styrene-acrylic
resin particle dispersion."
The content of the release agent microparticles in the release
agent dispersion is preferably 10 to 50 mass %, more preferably 15
to 40 mass %. A content of the release agent microparticles within
the above range leads to satisfactory hot offset resistance and
releasability of the toner.
(Coagulant)
The coagulant may be of any type and is preferably selected from
metal salts. Examples of the metal salts include salts of
monovalent metals, such as alkali metals (e.g., sodium, potassium,
and lithium); and salts of divalent metals (e.g., calcium,
magnesium, manganese, and copper); and salts of trivalent metals
(e.g., iron and aluminum). Specific examples of the metal salts
include sodium chloride, potassium chloride, lithium chloride,
calcium chloride, magnesium chloride, zinc chloride, copper
sulfate, magnesium sulfate, and manganese sulfate. Among these,
divalent metal salts are particularly preferred. The use of a small
amount of such a divalent metal salt can promote coagulation. These
coagulants may be used alone or in combination.
After addition of the coagulant in Step I, the resultant mixture is
preferably allowed to stand for only a short period of time until
the start of heating. Preferably, the mixture is heated to a
temperature equal to or higher than (the glass transition
temperature (T.sub.g-a) of the amorphous resin A+10).degree. C. and
equal to or lower than (the melting point (T.sub.m-c) of the
crystalline material+10).degree. C. immediately after the addition
of the coagulant. If the mixture is allowed to stand for a long
period of time before the heating, resin particles may fail to be
uniformly coagulated, leading to a variation in particle size
distribution of the toner matrix particles, and inconsistent
surface properties of the toner matrix particles. The mixture is
allowed to stand before the heating for typically 30 minutes or
less, preferably 10 minutes or less. The coagulant is preferably
added at a temperature equal to or lower than the glass transition
temperature of the amorphous resin, more preferably at room
temperature.
The heating rate in Step I is preferably 0.8.degree. C./min or
more. The upper limit of the heating rate may be any value, and is
preferably 15.degree. C./min for avoiding formation of coarse
particles due to rapid fusion. This heating promotes coagulation of
microparticles of the amorphous resin A and the colorant, to form
coagulated particles.
The coagulation and coalescence is preferably performed at an
appropriately controlled agitation rate. The control of the
agitation rate can reduce the collision and repulsion between
particles, to promote contact between the particles and coagulation
of the particles. The temperature of the mixture is preferably
higher than the melting point of the crystalline resin. While the
temperature of the mixture is maintained, the agitation rate is
appropriately controlled (e.g., the agitation rate is lowered) to
promote coagulation of the styrene-acrylic resin particles and the
colorant microparticles. After the particle size of the coagulated
particles reaches a desired value, the mixture is cooled in Step II
described below, and the coagulation is then stopped through
addition of a coagulation stopper, such as an aqueous solution of
salts, such as sodium chloride. The resultant coagulated particles
preferably have a volume median particle size of 4.5 to 7.0 .mu.m.
The volume median particle size of the coagulated particles can be
determined with an analyzer "Coulter Multisizer 3" (manufactured by
Beckman Coulter, Inc.).
<Crystalline Polyester Resin Dispersion>
In the present invention, a crystalline polyester resin dispersion
may be added to the coagulant-containing dispersion prepared in
Step I, and the styrene-acrylic resin, the release agent, and the
crystalline polyester resin are coagulated and coalesced together
under agitation, to prepare a core particle dispersion.
(Preparation of Crystalline Polyester Resin Dispersion)
The crystalline polyester resin dispersion is prepared through
synthesis of a crystalline polyester resin and then dispersion of
the crystalline polyester resin in the form of microparticles in an
aqueous medium. Thus, the crystalline polyester resin dispersion
may also be referred to as "crystalline polyester resin
microparticle dispersion" below.
The crystalline polyester resin can be prepared as in the
aforementioned process, and thus the redundant description is
omitted. The crystalline polyester resin preferably satisfies
Expression (A): 5.ltoreq.|C.sub.acid-C.sub.alcohol|.ltoreq.12 where
C.sub.alcohol represents the number of carbon atoms of a polyhydric
alcohol forming the resin and C.sub.acid represents the number of
carbon atoms of a polyvalent carboxylic acid forming the resin.
The crystalline polyester resin microparticle dispersion is
prepared through, for example, a process involving dispersion
treatment of the resin in an aqueous medium without use of an
organic solvent, or a process involving swelling and dissolution of
the resin in an organic solvent (e.g., ethyl acetate, methyl ethyl
ketone, toluene, or a general-purpose alcohol having a boiling
point of lower than 100.degree. C.), emulsification and dispersion
of the solution in an aqueous medium with a disperser, and then
removal of the solvent.
The crystalline polyester resin may have a carboxy group. In such a
case, ammonia or sodium hydroxide may be added to the crystalline
polyester resin solution for ionic dissociation of the carboxy
group contained in the resin and reliable and smooth emulsification
in the aqueous phase.
The aqueous medium may contain a dispersion stabilizer.
Alternatively, the aqueous medium may contain a surfactant or a
microparticulate resin for improving the dispersion stability of
oil droplets. The dispersion stabilizer, the surfactant, and the
microparticulate resin may be the same as described in the section
"preparation of styrene-acrylic resin particle dispersion."
The aforementioned dispersion treatment may be performed by use of
mechanical energy with any disperser described above in the section
"preparation of styrene-acrylic resin particle dispersion."
The crystalline polyester resin microparticles (oil droplets) in
the crystalline polyester resin microparticle dispersion prepared
as described above have a volume median particle size of preferably
50 to 1,000 nm, more preferably 50 to 500 nm, still more preferably
80 to 500 nm. The volume median particle size of the oil droplets
can be adjusted by, for example, control of the mechanical energy
during emulsification and dispersion.
The content of the crystalline polyester resin microparticles is
preferably 10 to 50 mass %, more preferably 15 to 40 mass %,
relative to the entire amount (100 mass %) of the crystalline
polyester resin microparticle dispersion. A content of the
crystalline polyester resin microparticles within the above range
leads to a narrow particles size distribution and an improvement in
properties of the toner.
[Step II]
Step II involves cooling the core particle dispersion prepared in
Step I to a temperature equal to or lower than the glass transition
temperature (T.sub.g-a) of the amorphous resin A.
The cooling temperature is preferably equal to or lower than (the
glass transition temperature (T.sub.g-a) of the amorphous resin
A-3).degree. C. If the cooling temperature is equal to or lower
than (T.sub.g-a-3).degree. C., the dispersion of the crystalline
material in the core particles is maintained during deposition and
coagulation of the shell resin particles, resulting in high image
quality. This is probably attributed to the fact that the
crystallinity of the crystalline material is ensured in the
amorphous resin matrix, and the dispersion of the material in the
core particles is maintained during deposition of the shell
particles. The lower limit of the cooling temperature may be any
value. The core particle dispersion is preferably cooled to ambient
temperature, since a large amount of energy for heat removal is
required for cooling the dispersion to room temperature or
lower.
The core particles contained in the dispersion cooled in Step II
preferably have a shape factor SF-2 of 105 to 140 because the shell
is prepared from a small amount of the amorphous resin B and the
resultant toner exhibits high compatibility between thermal
resistance during storage and low-temperature fixing
properties.
The shape factor SF-2 is preferably 107 to 135, preferably 110 to
130.
A shape factor SF-2 of more than 100 leads to avoidance of complete
coating of the core particles with the shells, resulting in
prevention of low releasability during fixation. A shape factor
SF-2 of less than 140 leads to avoidance of insufficient coating of
the core particles with the shells, resulting in satisfactory
thermal resistance during storage.
The lowest cooling temperature in Step II may be lower than
30.degree. C. The cooling temperature, however, is preferably
30.degree. C. or higher in view of production efficiency, since
further cooling does not greatly affect subsequent steps and
requires excessive heat exchange.
The cooling rate may be any value, but is preferably 0.2 to
20.degree. C./min, more preferably 1.0 to 10.degree. C./min. A
cooling rate falling with the above range leads to appropriate
control of the internal structure and shape of the core particles
in association with further crystallization of the crystalline
polyester resin in the core particles.
A cooling rate of 0.2.degree. C./min or more leads to prevention of
formation of core particles of irregular shape during further
crystallization of the crystalline polyester resin, resulting in a
desired shape of the toner.
A cooling rate of 20.degree. C./min or less leads to sufficient
crystallization of the crystalline polyester resin. Thus, excessive
fusion between the crystalline polyester resin and the amorphous
polyester resin can be prevented during coagulation of the shells,
resulting in appropriate formation of shell coats or coat domains.
The cooling may be performed by any process, such as a process
involving introduction of a cooling medium from outside into the
reaction vessel, or a process involving direct injection of cooling
water into the reaction system.
<Calculation of Shape Factor SF-2 of Core Particle>
For calculation of the shape factor SF-2, core particles are
separated from the core particle dispersion prepared in Step II and
then dried, and a cross-sectional image of the core particles is
captured. The shape factor SF-2 is calculated by Expression (1):
the shape factor SF-2 of a toner matrix particle=[(the perimeter of
the toner matrix particle).sup.2/(the projection area of the toner
matrix particle)].times.(1/4.pi.).times.100 Expression (1): A large
shape factor SF-2 of a particle indicates that the particle has a
very irregular shape. <Observation of Cross Section of Core
Particle> (Preparation of Section of Core Particle for
Observation)
Core particles are placed into a sample vial and stained with vapor
of ruthenium tetroxide (RuO.sub.4). The resultant particles are
dispersed in a photocurable resin (embedding resin) and then
photo-cured to form a block. The block is then sliced into an
ultrathin sample having a thickness of 60 to 100 nm.
(Observation of Cross Section of Core Particle)
The sliced sample is observed under the conditions described below.
The shape factor SF-2 of the core particles is calculated on the
basis of data prepared by 30-visual-field photographing of cross
sections having a diameter within a range of volume median particle
size (D50) of the core particles .+-.10%.
Apparatus: transmission electron microscope "JSM-7401F"
(manufactured by JEOL Ltd.)
Accelerating voltage: 30 kV
Magnification: 10,000 to 20,000
[Step III]
Step III involves adjusting the temperature of the core particle
dispersion to be equal to or higher than (the glass transition
temperature (T.sub.g-a) of the amorphous resin A+5).degree. C. and
equal to or lower than (the glass transition temperature
(T.sub.g-b) of the amorphous resin B+3).degree. C. after Step II,
and then adding a dispersion of the amorphous resin B to the core
particle dispersion.
More preferably, the temperature of the core particle dispersion is
adjusted to be equal to or higher than (the glass transition
temperature (T.sub.g-a) of the amorphous resin A+7).degree. C. and
equal to or lower than (the glass transition temperature
(T.sub.g-b) of the amorphous resin B+1).degree. C.
A temperature adjusted to be equal to or higher than (the glass
transition temperature (T.sub.g-a)+5).degree. C. is preferred in
view of productivity (i.e., prevention of a reduction in molecular
motion of the amorphous resin B, and shortening of the time for
deposition of particles of the amorphous resin B onto core
particles).
A temperature adjusted to be equal to or lower than
(T.sub.g-b+3).degree. C. leads to prevention of coagulation between
particles of the amorphous resin B and intrusion of the amorphous
resin B into the core particles, resulting in prevention of domain
formation (formation of large shell particles).
The amorphous resin B added in Step III is preferably in the form
of particles having a volume median particle size of 30 to 300
nm.
A volume median particle size of the amorphous resin B particles of
30 to 300 nm leads to even deposition of shell particles and
sufficient coating of the core particles with a small number of
shell particles. A volume median particle size of 30 nm or more
leads to prevention of coagulation between shell particles, whereas
a volume median particle size of 300 nm or less leads to sufficient
coating of the core particles with shell particles, resulting in
prevention of excessive exposure of the core particles.
The ratio of the mass of the amorphous resin B added in Step III to
the total mass of the binder resin is preferably 5 to 35, more
preferably 10 to 25, in view of improvements in thermal resistance
during storage and releasability during fixation of the toner. A
mass ratio of 5 or more leads to sufficient coating of the core
particles with the shells, resulting in further improved thermal
resistance during storage of the toner, whereas a mass ratio of 35
or less leads to higher thermal resistance and improved
releasability during fixation of the toner.
Expressions 1 and 2 are preferably satisfied in Step III:
pH.sub.b.ltoreq.pH.sub.a, and Expression 1:
2.ltoreq.pH.sub.b.ltoreq.5 Expression 2: where pH.sub.a represents
the pH of the core particle dispersion at 25.degree. C. before
addition of the amorphous resin B dispersion, and pH.sub.b
represents the pH of the amorphous resin B dispersion at 25.degree.
C. before being added to the core particle dispersion.
If Expressions 1 and 2 are satisfied, the amorphous resin B
particles are coagulated and deposited onto the core particles
while the coagulation between the amorphous resin B particles is
prevented. If Expressions 1 and 2 are satisfied, the amorphous
resin B particles can be evenly deposited onto the core particles,
resulting in formation of shells having uniform thickness and thus
improved thermal resistance during storage. From this viewpoint,
the pH.sub.a and pH.sub.b more preferably satisfy the following
expressions: 6.ltoreq.pH.sub.a.ltoreq.8 and
2.ltoreq.pH.sub.b.ltoreq.3. A pH.sub.a of less than 8 leads to
reduced coagulation between core particles, resulting in reduced
amount of residue.
In order to control the rate of coagulation between shell particles
and core particles after addition of the amorphous resin B
dispersion, the agitation rate may be adjusted, the core particle
dispersion may be heated/cooled to a temperature equal to or higher
than (the glass transition temperature (T.sub.g-a) of the amorphous
resin A+5).degree. C. and equal to or lower than (the glass
transition temperature (T.sub.g-b) of the amorphous resin
B+3).degree. C., and a pH adjuster may be used for adjustment of
the pH.sub.a and pH.sub.b to satisfy Expressions 1 and 2.
The pH adjuster may be any acid or alkali that dissolves in water.
Specific examples of the pH adjuster are described below.
Examples of the alkali include inorganic bases, such as sodium
hydroxide and potassium hydroxide, and ammonia.
Examples of the acid include inorganic acids, such as hydrochloric
acid, nitric acid, sulfuric acid, phosphoric acid, and boric acid;
sulfonic acids, such as methanesulfonic acid, ethanesulfonic acid,
and benzenesulfonic acid; and carboxylic acids, such as acetic
acid, citric acid, and formic acid.
(Measurement of pH)
The pH of the core particle dispersion at 25.degree. C. (pH.sub.a)
and the pH of the amorphous polyester resin particle dispersion at
25.degree. C. (pH.sub.b) before being added to the core particle
dispersion can be measured as described below.
In specific, the pH of the core particle dispersion at 25.degree.
C. and the pH of the amorphous polyester resin particle dispersion
at 25.degree. C. before being added to the core particle dispersion
can be measured with a glass-electrode hydrogen ion concentration
meter HM-20P (manufactured by DKK-TOA CORPORATION) (reference
electrode internal solution RE-4 calibrated with the following
three standard solutions: phthalate standard solution (pH 4.01,
25.degree. C.), neutral phosphate standard solution (pH 6.86,
25.degree. C.), and borate standard solution (pH 9.18, 25.degree.
C.)).
[Heating-Cooling Step]
After addition of the amorphous resin B dispersion, the resultant
dispersion of shell-deposited core particles is heated, and an
aqueous sodium chloride solution (i.e., a coagulation stopper) is
added to the dispersion, followed by fusion between core particles
and shell particles and fusion between shell particles. The
resultant product is then cooled to terminate the fusion of the
particles, to prepare a core-shell toner matrix particle
dispersion.
[Separation-Drying Step]
Core-shell toner matrix particles are separated from the core-shell
toner matrix particle dispersion and then dried.
The core-shell toner matrix particles may be separated from the
core-shell toner matrix particle dispersion by any known
technique.
For example, the separation step may involve any filtration
technique, such as centrifugation, filtration at reduced pressure
with a Nutsche filter, or filtration with a filter press.
The separated core-shell toner matrix particles may optionally be
washed. The washing step may involve removal of deposits (e.g., the
surfactant and the coagulant) from the separated core-shell toner
matrix particles (caked agglomeration of particles). The washing
step is preferably continued until the conductivity of the washings
reaches, for example, 1 to 10 .mu.S/cm.
The separated or washed core-shell toner matrix particles are then
dried. The drying step may be performed with any technique with,
for example, any known dryer. Examples of such dryers include spray
dryers, vacuum freeze dryers, reduced-pressure dryers, stationary
shelf dryers, mobile shelf dryers, fluidized bed dryers, rotary
dryers, and stirring dryers. The water content of the dried toner
matrix particles is preferably 5 mass % or less, more preferably 2
mass % or less.
If the dried core-shell toner matrix particles are coagulated by
weak interparticle force, the coagulated particles may be subjected
to disintegration treatment. This treatment may involve the use of
a mechanical disintegrator, such as a jet mill, a Henschel mixer, a
coffee mill, or a food processor.
[Application of External Additive]
An external additive may optionally be applied to the core-shell
toner matrix particles according to the present invention. This
step involves optional mixing of an external additive with the
dried core-shell toner matrix particles, to produce a toner. The
application of the external additive improves the fluidity,
charging properties, and cleanability of the toner.
<<Developer>>
The toner produced by the method of the present invention is
suitable for the following use. For example, the toner may be used
as a magnetic one-component developer containing a magnetic
material. Alternatively, the toner may be mixed with a carrier and
used as a two-component developer. Alternatively, the toner may be
used alone as a non-magnetic toner.
The carrier for forming the two-component developer may be magnetic
particles composed of any known material, such as a metal material
(e.g., iron, ferrite, or magnetite) or an alloy of such a metal and
aluminum or lead. Ferrite particles are particularly preferred.
The carrier has a volume average particle size of preferably 15 to
100 .mu.m, more preferably 25 to 60 .mu.m.
The carrier is preferably coated with a resin or in the form of a
dispersion of magnetic particles in a resin. Non-limiting examples
of the resin for coating of the carrier include olefinic resins,
cyclohexyl methacrylate-methyl methacrylate copolymers, styrenic
resins, styrene-acrylic resins, silicone resins, ester resins, and
fluororesins. Non-limiting examples of the resin for forming the
dispersion include known resins, such as acrylic resins,
styrene-acrylic resins, polyester resins, fluororesins, and
phenolic resins.
<<Fixation>>
The fixation of the toner of the present invention preferably
involves the use of a contact heating process. Examples of the
contact heating process include a thermal pressure fixing process,
a thermal roller fixing process, and a thermocompression fixing
process involving the use of a rotary pressure unit including a
fixed heater.
The aforementioned embodiments of the present invention should not
be construed to limit the invention, and various modifications of
the invention may be made.
The present invention may be appropriately modified without
departing from the scope of the invention.
EXAMPLES
The present invention will now be described in detail by way of
examples, which should not be construed to limit the present
invention. In the following examples, the term "parts" and the
symbol "%" refer to "parts by mass" and "mass %," respectively,
unless otherwise specified.
In toners 1 to 26, the melting point (T.sub.m-c) of a crystalline
material, the glass transition temperature (T.sub.g-a) of an
amorphous resin A, and the glass transition temperature (T.sub.g-b)
of an amorphous resin B were measured as described below.
[Measurement of Melting Point (T.sub.m-c) of Crystalline
Material]
The melting point of a crystalline material in the toner was
measured with a differential scanning calorimeter "Diamond DSC"
(manufactured by PerkinElmer, Inc.). In detail, a sample of the
toner (3.0 mg) was sealed in an aluminum pan and placed on a sample
holder of the calorimeter. The calorimetry was performed by the
following temperature program: a first heating process involving
heating from room temperature (25.degree. C.) to 150.degree. C. at
a rate of 10.degree. C./min and maintaining at 150.degree. C. for
five minutes; a cooling process involving cooling from 150.degree.
C. to 0.degree. C. at a rate of 10.degree. C./min and maintaining
at 0.degree. C. for five minutes; and a second heating process
involving heating from 0.degree. C. to 150.degree. C. at a rate of
10.degree. C./min. An empty aluminum pan was used as a
reference.
An endothermic curve prepared through the first heating process was
analyzed, and the maximum temperature of the endothermic peak of
the crystalline material was defined as the melting point T.sub.m-c
(.degree. C.) of the crystalline material. An exothermic curve
prepared through the cooling process was analyzed, and the maximum
temperature of the exothermic peak of the crystalline material was
defined as T.sub.q-c (.degree. C.).
[Measurement of Glass Transition Temperature T.sub.g of Amorphous
Resin]
The glass transition temperature (T.sub.g-a) of the amorphous resin
A and the glass transition temperature (T.sub.g-b) of the amorphous
resin B was determined with a differential scanning calorimeter
"Diamond DSC" (manufactured by PerkinElmer, Inc.). The temperature
of a sample was controlled through sequential processes of heating,
cooling, and heating (temperature range: 0 to 150.degree. C.,
heating rate: 10.degree. C./minute, cooling rate: 10.degree.
C./minute). The glass transition temperature was determined on the
basis of the data obtained through the second heating process. In
detail, the glass transition temperature corresponded to the
intersection of a line extending from the base line of the first
endothermic peak and a tangent corresponding to the maximum slope
between the rising point and maximum point of the first endothermic
peak.
[Preparation of Amorphous Resin Particle Dispersion S-1
(Styrene-Acrylic Resin Particles)]
A styrene-acrylic resin dispersion containing a release agent
disclosed in, for example, Japanese Patent No. 3915383 was used in
amorphous resin particle dispersion S-1. The dispersion was
prepared as detailed below.
(1) First Polymerization Step
Sodium dodecyl sulfate (8 parts by mass) and deionized water (3,000
parts by mass) were placed in a 5-L reactor equipped with an
agitator, a thermosensor, a cooling tube, and a nitrogen feeder,
and the mixture was agitated at 230 rpm under a nitrogen gas stream
while the internal temperature was raised to 80.degree. C. After
the temperature reached 80.degree. C., a solution of potassium
persulfate (10 parts by mass) in deionized water (200 parts by
mass) was added to the reactor, and the temperature of the mixture
was raised again to 80.degree. C. The following mixture of monomers
was added dropwise to the reactor over one hour, and the resultant
mixture was then heated and agitated at 80.degree. C. for two hours
for polymerization, to prepare resin microparticle dispersion
x1:
styrene, 480 parts by mass;
n-butyl acrylate, 250 parts by mass; and
methacrylic acid, 68 parts by mass.
(2) Second Polymerization Step
A solution of sodium polyoxyethylene (2) dodecyl ether sulfate (7
parts by mass) in deionized water (3,000 parts by mass) was placed
in a 5-L reactor equipped with an agitator, a thermosensor, a
cooling tube, and a nitrogen feeder, and was heated to 98.degree.
C. Resin microparticle dispersion x1 (260 parts by mass) and a
mixture prepared through dissolution of the following monomers and
release agent at 90.degree. C. was added to the heated
solution:
styrene (St), 284 parts by mass;
n-butyl acrylate (BA), 92 parts by mass;
methacrylic acid (MAA), 13 parts by mass;
n-octyl 3-mercaptopropionate, 3.0 parts by mass; and
release agent: behenyl behenate (melting point (T.sub.m-c):
73.degree. C.), 140 parts by mass. The resultant mixture was
processed for one hour in a mechanical disperser "CLEARMIX" having
a circulation path (manufactured by M Technique Co., Ltd.), to
prepare a dispersion containing emulsified particles (oil
droplets).
A solution of potassium persulfate (6 parts by mass) in deionized
water (200 parts by mass) (i.e., a polymerization initiator
solution) was added to the dispersion. The mixture was heated with
agitation for one hour at 84.degree. C. for polymerization, to
prepare resin microparticle dispersion x2.
(3) Third Polymerization Step
A solution of potassium persulfate (11 parts by mass) in deionized
water (400 parts by mass) was added to resin microparticle
dispersion x2. The composition of the following monomers was added
dropwise to the mixture over one hour at a temperature of
82.degree. C.:
styrene (St), 350 parts by mass;
n-butyl acrylate (BA), 215 parts by mass;
methacrylic acid (MAA), 20 parts by mass; and
n-octyl 3-mercaptopropionate, 8 parts by mass. After completion of
the dropwise addition, the resultant mixture was heated with
agitation for two hours for polymerization and was cooled to
28.degree. C., to prepare amorphous resin particle dispersion S-1
of vinyl resin (styrene-acrylic resin).
The amorphous resin particles contained in amorphous resin particle
dispersion S-1 had a volume median particle size of 210 nm, a glass
transition temperature (T.sub.g) (of dried matter) of 40.degree.
C., and a weight average molecular weight (Mw) of 33,000.
[Preparation of Amorphous Resin Particle Dispersion S-2
(Styrene-Acrylic Resin Particles)]
Sodium dodecyl sulfate (8 parts by mass) and deionized water (3,000
parts by mass) were placed in a 5-L reactor equipped with an
agitator, a thermosensor, a cooling tube, and a nitrogen feeder,
and the mixture was agitated at 230 rpm under a nitrogen gas stream
while the internal temperature was raised to 80.degree. C. After
the temperature reached 80.degree. C., a solution of potassium
persulfate (10 parts by mass) in deionized water (200 parts by
mass) was added to the reactor, and the temperature of the mixture
was raised again to 80.degree. C. The following mixture of monomers
was added dropwise to the reactor over one hour, and the resultant
mixture was then heated and agitated at 88.degree. C. for two hours
for polymerization, to prepare amorphous resin particle dispersion
S-2:
styrene, 460 parts by mass;
n-butyl acrylate, 250 parts by mass;
methacrylic acid, 88 parts by mass; and
n-octyl 3-mercaptopropionate, 7 parts by mass.
The amorphous resin particles contained in amorphous resin particle
dispersion S-2 had a volume median particle size of 103 nm, a glass
transition temperature (T.sub.g) (of dried matter) of 61.degree.
C., and a weight average molecular weight (Mw) of 28,000.
[Preparation of Colorant Dispersion]
Sodium dodecyl sulfate (90 parts by mass) was dissolved in
deionized water (1,600 parts by mass) with agitation, and carbon
black "MOGUL L" (manufactured by Cabot Corporation) (420 parts by
mass) was gradually added to the solution with agitation. The
carbon black was then dispersed in the solution with an agitator
"CLEARMIX" (manufactured by M Technique Co., Ltd.), to prepare
carbon black particle dispersion [Bk]. The carbon black particles
[Bk] contained in the dispersion had a volume median particle size
of 115 nm as determined with a particle size analyzer Microtrac
UPA-150 (manufactured by NIKKISO CO., LTD.).
[Preparation of Release Agent Dispersion]
Sodium polyoxyethylene (2) dodecyl ether sulfate (24 parts by mass)
was dissolved in deionized water (1,200 parts by mass) with
agitation. Behenyl behenate (240 parts by mass) used in S-1 was
gradually added to solution with agitation, and then dispersed in
the solution under heating with an agitator "CLEARMIX"
(manufactured by M Technique Co., Ltd.), to prepare a release agent
particle dispersion. The release agent particles contained in the
dispersion had a volume median particle size of 355 nm as
determined with a particle size analyzer Microtrac UPA-150
(manufactured by NIKKISO CO., LTD.).
[Preparation of Amorphous Resin Particle Dispersion P-1]
<Synthesis of Amorphous Polyester Resin p1>
The following monomers (including a bireactive monomer) for an
addition-polymerization resin (styrene-acrylic resin: St-Ac) unit
and a radical polymerization initiator were added to a dropping
funnel:
styrene, 80 parts by mass;
n-butyl acrylate, 20 parts by mass;
acrylic acid, 10 parts by mass; and
polymerization initiator (di-t-butyl peroxide), 16 parts by
mass.
The following monomers for a polycondensation resin (amorphous
polyester resin) unit were added to a four-neck flask equipped with
a nitrogen feeding tube, a dehydration tube, an agitator, and a
thermocouple, and were dissolved at 170.degree. C.:
propylene oxide (2 mol) adduct of bisphenol A, 255.5 parts by
mass;
ethylene oxide (2 mol) adduct of bisphenol A, 30.2 parts by
mass;
terephthalic acid, 56.3 parts by mass;
fumaric acid, 35.0 parts by mass; and
adipic acid, 22.0 parts by mass.
An esterification catalyst Ti(OBu).sub.4 (0.4 parts by mass) was
then added to the reaction system. The reaction system was heated
to 235.degree. C., and the reaction was allowed to proceed at
ambient pressure (101.3 kPa) for five hours and then at reduced
pressure (8 kPa) for one hour.
After the reaction system was cooled to 200.degree. C., the
monomers for the addition-polymerization resin were added dropwise
to the flask over 90 minutes with agitation and aged for 60
minutes. The unreacted monomers were then removed at reduced
pressure (8 kPa), and the reaction was continued until a desired
softening point was achieved, to prepare amorphous polyester resin
p1. Amorphous polyester resin p1 had a glass transition temperature
(T.sub.g) of 60.degree. C., a weight average molecular weight (Mw)
of 27,000, and a softening point of 109.degree. C.
[Preparation of Amorphous Resin Particle Dispersion P-1]
Amorphous polyester resin p1 (100 parts by mass) was dissolved in
ethyl acetate (manufactured by Kanto Chemical Co., Inc.) (400 parts
by mass), and was mixed with a preliminarily prepared 0.4 mass %
sodium lauryl sulfate solution (638 parts by mass). The mixed
solution was ultrasonically dispersed with an ultrasonic
homogenizer "US-150T" (manufactured by NIHONSEIKI KAISHA LTD.) at a
V-LEVEL of 300 .mu.A for 35 minutes with agitation. While the
dispersion was maintained at 40.degree. C., ethyl acetate was
completely removed with a diaphragm vacuum pump "V-700"
(manufactured by BUCHI) with agitation at reduced pressure for
three hours, to prepare amorphous resin particle dispersion P-1
(solid content: 13.5 mass %). The particles contained in amorphous
resin particle dispersion P-1 had a volume median particle size
("particle size" in TABLE 1) of 120 nm.
[Preparation of Amorphous Resin Particle Dispersion P-2 (Amorphous
Polyester Resin Dispersion)]
<Synthesis of Amorphous Polyester Resin p2>
Amorphous polyester resin p2 was synthesized as in amorphous
polyester resin p1, except that the monomers for a polycondensation
resin were modified as follows:
fumaric acid, 30.0 parts by mass; and
adipic acid, 27.0 parts by mass.
The reaction was continued until a softening point of 96.degree. C.
was achieved to prepare amorphous polyester resin p2. Amorphous
polyester resin p2 had a glass transition temperature (T.sub.g) of
43.degree. C. and a weight average molecular weight (Mw) of
16,000.
<Preparation of Amorphous Resin Particle Dispersion P-2>
Amorphous resin particle dispersion P-2 was prepared as in
amorphous resin particle dispersion P-1, except that amorphous
polyester resin p1 was replaced with amorphous polyester resin p2.
The particles contained in amorphous resin particle dispersion P-2
had a volume median particle size of 130 nm.
[Preparation of Crystalline Resin Particle Dispersion C1
(Crystalline Polyester Resin Particle Dispersion)]
<Synthesis of Crystalline Polyester Resin c1>
1,14-Tetradecanedicarboxylic acid (281 parts by mass) and
1,6-hexanediol (259 parts by mass) were placed in a reactor
equipped with an agitator, a thermometer, a cooling tube, and a
nitrogen gas feeding tube. After the reactor was purged with dry
nitrogen gas, an esterification catalyst Ti(OBu).sub.4 (0.1 parts
by mass) was added to the mixture, and the mixture was agitated for
about eight hours under a nitrogen gas stream at about 180.degree.
C.
The following monomers (including a bireactive monomer) for an
addition-polymerization resin (styrene-acrylic resin: StAc) unit
and a radical polymerization initiator were added to a dropping
funnel:
styrene, 34 parts by mass;
n-butyl acrylate, 12 parts by mass;
acrylic acid, 2 parts by mass; and
polymerization initiator (di-t-butyl peroxide), 7 parts by
mass.
The monomers for the addition-polymerization resin (StAc) were
added dropwise to the flask over 90 minutes with agitation and aged
for 60 minutes, and then the unreacted monomers were removed at
reduced pressure (8 kPa). The ratio of the amount of the removed
monomers to that of the added monomers was very low. An
esterification catalyst Ti(OBu).sub.4 (0.8 parts by mass) was then
added to the reaction system. The reaction system was heated to
235.degree. C., and the reaction was allowed to proceed at ambient
pressure (101.3 kPa) for five hours and then at reduced pressure (8
kPa) for one hour.
After the reaction system was cooled to 200.degree. C., the
reaction was continued at reduced pressure (20 kPa) for 1.5 hours,
to prepare crystalline polyester resin c1 (i.e., hybrid crystalline
polyester resin). The content of StAc unit (other than CPEs) was 10
mass % relative to the entire amount of crystalline polyester resin
c1. Crystalline polyester resin c1 had a structure composed of CPEs
grafted to StAc. Crystalline polyester resin c1 had a number
average molecular weight (Mn) of 4,900 and a melting point
(T.sub.m-c) of 73.degree. C.
[Preparation of Crystalline Resin Particle Dispersion C1]
Crystalline polyester resin c1 (30 parts by mass) was melted and
transferred to an emulsifier "Cavitron CD1010" (manufactured by
EUROTEC LIMITED) at a rate of 100 parts by mass/min. Aqueous
ammonia (70 parts by mass) was diluted with deionized water in an
aqueous solvent tank. While being heated with a heat exchanger at
100.degree. C., the diluted aqueous ammonia (concentration: 0.37
mass %) was transferred to the emulsifier "Cavitron CD1010" at a
rate of 0.1 L/min simultaneous with the transfer of crystalline
polyester resin c1. The emulsifier "Cavitron CD1010" was operated
at a rotor speed of 60 Hz and a pressure of 490.3 kPa (5
kg/cm.sup.2), to prepare crystalline resin particle dispersion C1
(solid content: 30 parts by mass). The particles contained in
crystalline resin particle dispersion C1 had a volume median
particle size of 220 nm.
[Preparation of Toner Matrix Particles 1]
Amorphous resin particle dispersion S-1 (200 parts by mass in terms
of solid content), the colorant dispersion (20 parts by mass in
terms of solid content), and deionized water (2,000 parts by mass)
were placed in a reactor equipped with an agitator, a thermosensor,
and a cooling tube. A 5 mol/L aqueous sodium hydroxide solution was
then added to the reactor to adjust the pH of the mixture to 10. A
solution of magnesium chloride (60 parts by mass) in deionized
water (60 parts by mass) was added to the mixture in the reactor
with agitation at 25.degree. C. over 10 minutes.
The resultant mixture was heated with agitation to 75.degree. C.
("coagulation and coalescence temperature" in TABLE 2), and the
agitation rate was appropriately controlled. The particle size of
associated particles was determined with a particle size analyzer
"Coulter Multisizer 3" (manufactured by Beckman Coulter, Inc.). The
coagulation and coalescence of the associated particles was
continued until the volume median particle size of the particles
reached 5.8 .mu.m, and then the agitation rate was adjusted to
terminate the coagulation. The coagulation and coalescence
temperature was maintained for one hour to prepare a core particle
dispersion (Step I).
The core particle dispersion was then cooled to 35.degree. C.
("cooling temperature" in TABLE 2) (Step II). A 5 mol/L aqueous
sodium hydroxide solution was added to the dispersion to adjust the
pH to 7 (at 25.degree. C.), and then the resultant mixture was
heated to 61.degree. C. ("temperature during addition of amorphous
resin B" in TABLE 2). Amorphous resin particle dispersion P-1
(i.e., amorphous resin B dispersion) (pH 2) (200 parts by mass in
terms of solid content) was added to the mixture over 20 minutes
(Step III). After confirmation of the deposition of shell particles
(i.e., amorphous resin B particles) onto core particles, the
resultant dispersion was heated to 73.degree. C.
A solution of sodium chloride (120 parts by mass) in deionized
water (650 parts by mass) was added to the dispersion, and the
fusion of the particles was allowed to proceed while the volume
median particle size of the particles was maintained. The average
sphericity of the particles contained in the dispersion was
determined with a particle image analyzer "FPIA-3000" (manufactured
by Sysmex Corporation) (4000 particles detected in a high-power
field (HPF)). After the average sphericity reached 0.963, the
dispersion was cooled to 35.degree. C. to terminate the fusion of
the particles.
Toner dispersion 1 containing toner matrix particles 1 was thereby
prepared.
Toner matrix particles 1 were separated from toner dispersion 1,
washed, and then dried until a water content of less than 1% was
achieved.
<Calculation of Shape Factor SF-2 of Core Particle>
Core particles were separated from the core particle dispersion
prepared in Step II and then dried, and a cross-sectional image of
the core particles was captured as described below. The shape
factor SF-2 of the core particles was calculated by Expression (1).
The results are illustrated in TABLE 2. the shape factor SF-2 of a
toner matrix particle=[(the perimeter of the toner matrix
particle).sup.2/(the projection area of the toner matrix
particle)].times.(1/4.pi.).times.100 Expression (1):
<Observation of Cross Section of Core Particle> (Preparation
of Section of Core Particle for Observation)
Core particles (0.2 to 1 g) were placed into a 10-mL sample vial
and stained with vapor of ruthenium tetroxide (RuO.sub.4) as
described below. The resultant particles were dispersed in a
photocurable resin "D-800" (manufactured by JEOL Ltd.) and then
photo-cured to form a block. The block was then sliced with a
microtome having a diamond blade into an ultrathin sample having a
thickness of 60 to 100 nm.
The sample was optionally treated with ruthenium tetroxide in view
of ease of observation. The ruthenium tetroxide treatment involves
the use of a vacuum electron staining apparatus VSC1R1
(manufactured by Filgen, Inc.). In detail, the toner or ultrathin
sample was introduced into a ruthenium tetroxide-containing
sublimation chamber (staining chamber) provided in the apparatus,
and then stained with ruthenium tetroxide at room temperature (24
to 25.degree. C.) and concentration level 3 (300 Pa) for 10
minutes.
<Observation of Cross Section of Core Particle>
The stained sample was observed under the conditions described
below. The shape factor SF-2 of the core particles was calculated
on the basis of data prepared by 30-visual-field photographing of
cross sections having a diameter within a range of volume median
particle size (D50) of the core particles .+-.10%.
Apparatus: transmission electron microscope "JSM-7401F"
(manufactured by JEOL Ltd.)
Accelerating voltage: 30 kV
Magnification: 10,000
[Preparation of Toner Matrix Particles 2 to 5 and 7 to 26]
Toner matrix particles 2 to 5 and 7 to 26 were prepared as in toner
matrix particles 1, except that the conditions for the preparation
were modified as illustrated in TABLEs 1 and 2. TABLE 1 also
illustrates the proportion of the mass of the amorphous resin A,
the crystalline resin, or the amorphous resin B to the total mass
of the binder resin (i.e., the total mass of the amorphous resin A,
the crystalline resin, and the amorphous resin B) (the proportion
will be referred to as "mass ratio" in TABLE 1).
[Preparation of Toner Matrix Particles 6]
Amorphous resin particle dispersion S-1 (200 parts by mass in terms
of solid content), the colorant dispersion (20 parts by mass in
terms of solid content), and deionized water (2,000 parts by mass)
were placed in a reactor equipped with an agitator, a thermosensor,
and a cooling tube. A 5 mol/L aqueous sodium hydroxide solution was
then added to the reactor to adjust the pH of the mixture to 10. A
solution of magnesium chloride (60 parts by mass) in deionized
water (60 parts by mass) was added to the mixture with agitation at
25.degree. C. over 10 minutes.
The resultant mixture was heated with agitation to 75.degree. C.,
and crystalline resin particle dispersion C1 (20 parts by mass in
terms of solid content) was added to the mixture over 20 minutes.
The agitation rate was appropriately controlled, and the particle
size of associated particles was determined with a particle size
analyzer "Coulter Multisizer 3" (manufactured by Beckman Coulter,
Inc.). The coagulation of the associated particles was continued
until the volume median particle size of the particles reached 5.8
.mu.m, and then the agitation rate was adjusted to terminate the
coagulation. The resultant mixture was heated to 75.degree. C. and
maintained at the temperature for one hour, to prepare a core
particle dispersion (Step I).
The core particle dispersion was cooled to 35.degree. C. (Step II),
and then a 5 mol/L aqueous sodium hydroxide solution was added to
the dispersion to adjust the pH to 7 (at 25.degree. C.). The
resultant mixture was heated to 61.degree. C., and amorphous resin
particle dispersion P-1 (pH 2) was added to the mixture over 20
minutes (Step III). After confirmation of the coagulation and
deposition of shell particles onto core particles, a solution of
sodium chloride (100 parts by mass) in deionized water (760 parts
by mass) was added to the mixture to terminate the growth
(coagulation) of the particles. The resultant dispersion was heated
and agitated at 72.degree. C. to allow the fusion of the particles
to proceed. The average sphericity of the particles contained in
the dispersion was determined with a particle image analyzer
"FPIA-3000" (manufactured by Sysmex Corporation) (4000 particles
detected in a high-power field (HPF) mode). After the average
sphericity reached 0.963, the dispersion was cooled to 35.degree.
C. to terminate the fusion of the particles. Toner dispersion 6
containing toner matrix particles 6 was thereby prepared.
Toner matrix particles 6 were separated from toner dispersion 6,
washed, and then dried until a water content of less than 1%.
TABLE-US-00001 TABLE 1 Constitution Core particle Toner Crystalline
material Shell matrix Amorphous resin A Release agent Crystalline
resin Amorphous resin B particle Dispersion T.sub.g-b Mass
T.sub.m-c Dispersion Mass T.sub.m-c Di- spersion Particlesize
T.sub.g-b No. No. [.degree. C.] ratio Type [.degree. C.] No. ratio
[.degree. C.] No. [nm] [.degree. C.] Mass ratio Note 1 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 2 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 3 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 4 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 5 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 6 S-1 40 78
Behenyl behenate 73 C-1 7 73 P-1 120 60 15 Example 7 S-1 40 94
Behenyl behenate 73 -- -- -- P-1 120 60 6 Example 8 S-1 40 70
Behenyl behenate 73 -- -- -- P-1 120 60 30 Example 9 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 10 P-2 43 85
Behenyl behenate 73 -- -- -- S-2 103 61 15 Example 11 P-2 43 85
Behenyl behenate 73 -- -- -- S-2 103 61 15 Example 12 P-2 43 87
Behenyl behenate 73 -- -- -- S-2 103 61 13 Example 13 P-2 43 87
Behenyl behenate 73 -- -- -- S-2 103 61 13 Example 14 P-2 43 87
Behenyl behenate 73 -- -- -- S-2 103 61 13 Example 15 P-2 43 87
Behenyl behenate 73 -- -- -- S-2 103 61 13 Example 16 P-2 43 94
Behenyl behenate 73 -- -- -- S-2 103 61 6 Example 17 P-2 43 70
Behenyl behenate 73 -- -- -- S-2 103 61 30 Example 18 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 19 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Example 20 S-1 40 85
Behenyl behenate 73 -- -- -- P-1 120 60 15 Comparative Example 21
S-1 40 85 Behenyl behenate 73 -- -- -- P-1 120 60 15 Comparative
Example 22 S-1 40 85 Behenyl behenate 73 -- -- -- P-1 120 60 15
Comparative Example 23 S-1 40 85 Behenyl behenate 73 -- -- -- P-1
120 60 15 Example 24 P-2 43 87 Behenyl behenate 73 -- -- -- S-2 103
61 13 Comparative Example 25 P-2 43 87 Behenyl behenate 73 -- -- --
S-2 103 61 13 Comparative Example 26 P-2 43 87 Behenyl behenate 73
-- -- -- S-2 103 61 13 Comparative Example
TABLE-US-00002 TABLE 2 Production conditions Step I Coagulation
Step III Toner and Step II Temperature matrix coalescence Cooling
during addition of particle temperature Temperature amorphous resin
B No. [.degree. C.] [.degree. C.] SF-2 [.degree. C.] pH.sub.a
pH.sub.a Note 1 75 35 137 61 7 2 Example 2 78 35 121 61 7 2 Example
3 82 35 107 61 7 2 Example 4 78 40 122 61 7 2 Example 5 78 35 121
61 6 5 Example 6 75 35 126 61 7 2 Example 7 78 35 123 61 7 2
Example 8 78 35 119 61 7 2 Example 9 78 35 121 63 6.5 2 Example 10
68 39 135 62 6.5 3 Example 11 75 39 108 62 6.5 3 Example 12 73 38
120 61 6.5 3 Example 13 73 38 119 61 6 5 Example 14 73 43 121 61
6.5 3 Example 15 73 38 120 64 6.5 3 Example 16 73 38 126 61 6.5 3
Example 17 73 38 118 61 6.5 3 Example 18 53 35 140 61 7 2 Example
19 75 35 121 48 7 2 Example 20 84 35 104 61 7 2 Comparative Example
21 78 78 121 78 7 2 Comparative Example (No cooling) 22 78 35 121
66 7 2 Comparative Example 23 78 35 121 61 7 6 Example 24 84 35 147
61 7 2 Comparative Example 25 73 7 120 73 6.5 3 Comparative Example
(No cooling) 26 73 35 121 66 6.5 3 Comparative Example
[Production of Toner 1]
Hydrophobic silica (number average primary particle size: 12 nm,
hydrophobicity: 68) (0.6 parts by mass) and hydrophobic titanium
oxide (number average primary particle size: 20 nm, hydrophobicity:
63) (1.0 part by mass) were added to toner matrix particles 1 (100
parts by mass), and were mixed with a Henschel mixer (manufactured
by Nippon Coke & Engineering Co., Ltd.) at a circumferential
velocity of a rotary blade of 35 mm/sec and 32.degree. C. for 20
minutes. Coarse particles were then removed with a sieve having an
opening of 45 .mu.m, followed by treatment with an external
additive, to produce toner 1.
[Production of Toners 2 to 26]
Toners 2 to 26 were produced as in toner 1, except that toner
matrix particles 1 were replaced with toner matrix particles 2 to
26.
[Production of Developers 1 to 26]
Developers 1 to 26 used for evaluation of toners 1 to 26 were
produced as described below.
(1) Preparation of Carrier
Ferrite core particles (100 parts by mass) and cyclohexyl
methacrylate-methyl methacrylate (5:5) copolymer resin
microparticles (5 parts by mass) were mixed with agitation in a
high-speed mixer equipped with a stirring blade at 120.degree. C.
for 30 minutes. Resin coating layers were formed on the surfaces of
the ferrite core particles through application of mechanical impact
force, to prepare a carrier having a volume median particle size of
35 .mu.m.
The volume median particle size of the carrier was measured with a
laser diffraction particle size analyzer "HELOS" (manufactured by
SYMPATEC) equipped with a wet disperser.
(2) Mixing of Toner and Carrier
The carrier was mixed with each of toners 1 to 26 (toner
concentration: 6.5 mass %) in a micro V-type mixer (manufactured by
Tsutsui Scientific Instruments Co., Ltd.) at a rotation rate of 45
rpm for 30 minutes. Developers 1 to 26 were thereby produced.
[Evaluation]
<Evaluation Apparatus>
Each developer was placed into a developing unit of a commercial
color copier "bizhub PRO C1060" (manufactured by KONICA MINOLTA,
INC.), and test images were formed for evaluation of the
developer.
<Evaluation of Low-Temperature Fixing Properties (Under
Offset)>
The under offset is an image defect involving detachment of a toner
from a transfer medium (e.g., a sheet) due to insufficient fusion
of the toner heated by a fixing unit.
Each of developers 1 to 26 was placed into the developing unit for
evaluation of low-temperature fixing properties. The color copier
was modified such that the fixing temperature, the amount of a
toner to be deposited, and the system rate were adjustable. In
detail, a solid image (toner density: 11.3 g/m.sup.2) was printed
on sheets NPI (128 g/m.sup.2) (manufactured by Nippon Paper
Industries Co., Ltd.) with the modified apparatus. The fixation
rate was adjusted to 300 mm/sec, the temperature of a fixing belt
was varied from 100 to 200.degree. C. in 5.degree. C. increments,
and the temperature of a fixing roller was adjusted to 100.degree.
C. The temperature of the fixing belt was measured during fixation,
and the minimum fixing temperature at which no under offset
occurred was determined for evaluation of low-temperature fixing
properties. A lower minimum fixing temperature indicates superior
low-temperature fixing properties. A developer exhibiting a minimum
fixing temperature of lower than 145.degree. C. was acceptable.
(Evaluation Criteria)
A: A minimum fixing temperature of lower than 120.degree. C.
B: A minimum fixing temperature of 120.degree. C. or higher and
lower than 135.degree. C.
C: A minimum fixing temperature of 135.degree. C. or higher and
lower than 145.degree. C.
D: A minimum fixing temperature of 145.degree. C. or higher
<Thermal Resistance During Storage>
A toner (0.5 g) was placed in a 10-mL glass vial having an inner
diameter of 21 mm. The vial was sealed with a lid and was shaken
600 times at room temperature with Tap Denser KYT-2000
(manufactured by Seishin Enterprise Co., Ltd.). The lid was
removed, and the vial was left at 57.5.degree. C. and 35% RH for
two hours. Subsequently, the toner was carefully placed on a
48-mesh sieve (opening: 350 .mu.m) to prevent disintegration of
coagulated toner. The sieve was set on a powder tester
(manufactured by Hosokawa Micron) and was fixed with a presser bar
and a knob nut. The intensity of vibration was adjusted (vibration
width: 1 mm), and the sieve was vibrated for 10 seconds. The
proportion (mass %) of the residual toner on the sieve was
determined.
The toner coagulation rate was calculated from Expression (A):
toner coagulation rate (%)=[(mass (g) of the residual toner on the
sieve)/0.5 (g)].times.100 Expression (A):
The thermal resistance during storage of a toner was evaluated on
the basis of the following criteria.
(Evaluation Criteria)
A: a toner coagulation rate of less than 10 mass % (very high
thermal resistance during storage of toner)
B: a toner coagulation rate of 10 mass % or more and less than 15
mass % (high thermal resistance during storage of toner)
C: a toner coagulation rate of 15 mass % or more and less than 20
mass % (slightly poor thermal resistance during storage of toner,
practically acceptable)
D: a toner coagulation rate of 20% or more (poor thermal resistance
during storage of toner, practically unacceptable)
<Releasability During Fixation>
Paper sheets used for evaluation (Kinfuji, 85 g/m.sup.2, long-grain
paper) (manufactured by Oji Paper Co., Ltd.) were conditioned at
normal temperature and normal humidity (NN environment: 25.degree.
C., 50% RH) overnight. Entirely solid images with different toner
densities (g/m.sup.2) were printed on the sheets under the
following fixation conditions: top margin: 5 mm, upper press
temperature: 195.degree. C., and lower press temperature:
120.degree. C. The toner density (g/m.sup.2) of the solid image
immediately before occurrence of paper jam was determined and
defined as "critical toner density" for evaluation of releasability
during fixation. A higher critical toner density indicates superior
releasability. A toner exhibiting a critical toner density of 2.5
g/m.sup.2 or more was acceptable. This test was performed at normal
temperature and normal humidity (NN environment: 25.degree. C., 50%
RH).
The releasability during fixation of a toner was evaluated on the
basis of the following criteria.
(Evaluation Criteria)
A: a critical toner density of 4.5 g/m.sup.2 or more (very high
releasability during fixation of toner)
B: a critical toner density of 3.5 g/m.sup.2 or more and less than
4.5 g/m.sup.2 (high releasability during fixation of toner)
C: a critical toner density of 2.5 g/m.sup.2 or more and less than
3.5 g/m.sup.2 (practically acceptable releasability during fixation
of toner)
D: a critical toner density of less than 2.5 g/m.sup.2 (poor
releasability during fixation of toner, practically
unacceptable)
<HH Transfer Efficiency>
A solid image (test image) (10 cm.times.10 cm) were printed on
paper sheets at high temperature and high humidity (HH environment:
30.degree. C., 80% RH). The mass of a toner deposited on the
photoreceptor (W before transfer) and the mass of a toner
transferred and deposited onto a paper sheet (W after transfer)
were measured, and the transfer rate was calculated by Expression
(B) described below for evaluation of HH transfer efficiency. The
results are shown in TABLE 3. A toner exhibiting a transfer rate of
85% or more was acceptable. transfer rate (%)=[(W after
transfer)/(W before transfer)].times.100 Expression (B):
(Evaluation Criteria)
B: 90% or more
C: 85% or more and less than 90%
D: less than 85%
<GI (Image Roughness)>
For evaluation of developers 1 to 26, a commercial color copier
"bizhub PRO C1060" (manufactured by KONICA MINOLTA, INC.) was
modified such that the surface temperature of a heating roller in a
fixing unit was varied within a range of 100 to 200.degree. C. The
surface temperature of the heating roller was adjusted to the
lowest fixing temperature (i.e., higher one of the aforementioned
low-temperature offset temperature and the lower limit of the
fixing temperature), and a solid image (100% image) (toner density:
10 mg/cm.sup.2) and a 50% shaded image were printed on an art
(coated) sheet (basis weight: 250 g/m.sup.2). The graininess index
(GI) of the 50% shaded image was determined with an image analyzing
system "GI-es-8500AAC" (manufactured by NATIONAL INSTRUMENT). A GI
of less than 0.22 indicates that the toner provides a practically
acceptable image with reduced roughness.
(Evaluation Criteria)
B: less than 0.20
C: 0.20 or more and less than 0.22
D: 0.22 or more
TABLE-US-00003 TABLE 3 Toner matrix Results of evaluation Toner
particle Low-temperature Thermal resistance Releasability HH
transfer GI No. No. fixing properties during storage during
fixation efficiency value Note 1 1 B B B C C Example 2 2 B A B B B
Example 3 3 C A C B B Example 4 4 B B B C B Example 5 5 C B B C C
Example 6 6 A B B B B Example 7 7 B C C B B Example 8 8 C A A C B
Example 9 9 B B B C C Example 10 10 A C B C C Example 11 11 B B C B
B Example 12 12 B B B B B Example 13 13 C B B C B Example 14 14 B B
B C C Example 15 15 B B C C C Example 16 16 A C C C C Example 17 17
C A B B B Example 18 18 B C B C C Example 19 19 B C B C B Example
20 20 C B D B B Comparative Example 21 21 B D B D D Comparative
Example 22 22 B C C D D Comparative Example 23 23 B C B C C Example
24 24 B C B D D Comparative Example 25 25 B C B D D Comparative
Example 26 26 B C B D D Comparative Example
As illustrated in TABLE 3, the method of the present invention can
produce a toner for developing electrostatic images, the toner
having high compatibility between thermal resistance during storage
and low-temperature fixing properties, exhibiting improved charging
properties, and providing high-quality images.
* * * * *